This story contains graphic images, including some of child victims.

(CNN) Fresh airstrikes rained down Wednesday on a rebel-held neighborhood in Syria's east Aleppo, killing two people at a market where an alleged chlorine gas attack injured more than 100 people a day earlier, an activist told CNN.

The two at the market were among at least seven people killed and 40 injured in the latest strikes on the Sukkari neighborhood, the activist with the Aleppo Media Center said. The center is a group of opposition-affiliated activists documenting the conflict in the city.

In Tuesday's alleged chemical attack, more than 100 people -- including dozens of children -- were admitted to the hospital after barrels suspected of containing chlorine gas were dropped, medical group activists say.

Wednesday's airstrikes struck the market, a mosque, a street and a roundabout in the rebel-occupied neighborhood, the activist said.

He described scenes of terror at the market as he arrived in the aftermath.

"People were very afraid," he said. He told of a boy and a girl crying as they searched for their father, a sandwich seller, and emergency vehicles speeding in fear of further strikes from military jets overhead.

There were desperate scenes at a hospital where a team of two doctors and two nurses tended to people's injuries.

"It was another massacre," the activist said.

Children injured in alleged chlorine attack

Chlorine gas allegedly was dropped about 1 p.m. local time Tuesday in barrel bombs from a helicopter, according to another Aleppo Media Center activist who attended the aftermath of the blast.

The drop was followed by four rockets fired by military jets, he said.

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"When I arrived at the market, I started seeing the injured people and noticed that something was unusual," he said.

"The injured did not have any signs of injuries or blood," he said, but instead were coughing loudly and had red, teary eyes.

"From 300 meters from the center of the barrel bomb, I started smelling chlorine, and I realized it was a chlorine bomb," he said.

One person was killed by the blast of the barrel bomb, according to the US-based Syrian American Medical Society , which supports one of three hospitals in Aleppo where the victims were taken.

In this still from a video, a girl is treated at a makeshift hospital after the suspected chemical attack.

At least 37 children and 10 women were among those hospitalized, the Aleppo Free Doctors Committee said in a statement.

The victims were struggling to breathe, coughing harshly, and they had the smell of chlorine on their clothes, the statement said.

Most were discharged after several hours, but 10 people remained in intensive care, including a pregnant woman in her last trimester whose unborn child was showing a weak pulse, the committee said.

CNN cannot confirm the authenticity of these reports.

Another reported use of chlorine gas in besieged eastern #Aleppo City. Casualties include many children. pic.twitter.com/HTQ2jcL0kJ — SAMS (@sams_usa) September 6, 2016

Medical sources point to regime

Harrowing footage distributed by the Syrian Civil Defense -- a volunteer group also known as the White Helmets -- showed young children and others being rushed to the hospital in the arms of rescuers, gasping desperately for air while being given oxygen masks.

Footage purporting to be of the blast site moments afterward showed barrels lying on top of what's left of destroyed buildings.

In the video, rescuers washed a boy with a hose after he was pulled from the rubble as sirens wail around him.

The UK-based Syrian Observatory for Human Rights also reported the attack, saying that medical sources accused regime warplanes of pounding the Sukkari neighborhood with barrel bombs "laden with poison gas."

The Syrian government has denied using chlorine gas for military purposes in the past.

Expert sees resurgence in chemical weapons

Hamish de Bretton-Gordon, a chemical weapons expert who is an adviser to nongovernmental organizations in Syria and Iraq, said chlorine gas could be deadly, and was a powerful psychological weapon.

What happens when chlorine is used as a chemical weapon? Chlorine, element 17 on the periodic table, is a so-called dual-use chemical with a number of industrial uses. Fatal in high concentrations and harmful in lower doses, chlorine gas can also be used as a crude weapon. The chemical was widely used in the First World War. When inhaled, it reacts with water in the body to produce corrosive hydrochloric acid that damages human cells. The effects can begin within seconds to minutes, causing victims to experience difficulty breathing, chest tightness, coughing and eye and skin irritation. Inhaling high levels of chlorine can cause pulmonary edema -- when fluid builds up in the lungs. In conflict situations, delivery methods include dropping chlorine gas onto civilian areas from aircraft via improvised barrel bombs.

The use of the widely available chemical in warfare was a war crime, he said.

"It's not nearly as toxic as nerve agents like sarin. It's a choking agent, and if you breathe enough of it, it creates hydrochloric acid," he said.

"Children's lungs are much more susceptible. That's one of the reasons you see much more child casualties than adults."

He said the Syrian conflict has seen a resurgence in chemical weapons, which had not been widely used since the Iran-Iraq War and Saddam Hussein's campaign against the Kurds in the late 1980s.

The international community took no military action in response, although a multinational deal was struck under which the majority of Syria's chemical arsenal was removed.

However, the deal did not remove stocks of chlorine, a dual-use chemical that has industrial applications but can also be used as a crude chemical weapon, delivered by improvised barrel bomb.

"The barrel bombs are basically liquid cylinders of chlorine that they throw out a helicopter," de Bretton-Gordon said.

"You don't even need a very big explosive -- just enough to split the barrel."

Photos: Aleppo photographer watches city die Two children walk past a "White Helmet" soon after an airstrike hits the Shaar neighborhood of Aleppo. Hide Caption 1 of 10 Photos: Aleppo photographer watches city die Members of the "White Helmets" civil defense volunteers carry the body of a man killed in a Russian airstrike in Andan town in the countryside north of of Aleppo. Hide Caption 2 of 10 Photos: Aleppo photographer watches city die Buses piled one on top of the other offer some protection from enemy fire. Hide Caption 3 of 10 Photos: Aleppo photographer watches city die Keeping the lights on: The electricity "operations room" in a neighborhood of rebel-held Aleppo. Hide Caption 4 of 10 Photos: Aleppo photographer watches city die Two men and their donkey navigate the bombed alleyways of Almarja district in eastern Aleppo. Hide Caption 5 of 10 Photos: Aleppo photographer watches city die A mother watches over her children as they return from school; the massive sheet hanging in the street is to deter government snipers. Hide Caption 6 of 10 Photos: Aleppo photographer watches city die A street that is monitored by regime snipers. Hide Caption 7 of 10 Photos: Aleppo photographer watches city die A stall holder waits for customers; there are reports of some hoarding of rice and flour as the regime's siege tightens. Hide Caption 8 of 10 Photos: Aleppo photographer watches city die A street market in Aleppo that is still open despite constant airstrikes -- and the huge slab of concrete hanging over it. Hide Caption 9 of 10 Photos: Aleppo photographer watches city die There is still fresh produce in the market stalls but it is more difficult to bring into the city, and much more expensive than even a few weeks ago. Hide Caption 10 of 10

Since the Ghouta attack, he estimated that chemical weapons had been used more than 100 times in the conflict, and their effectiveness when deployed by the regime against ISIS had encouraged the terror group to use them in turn.

"Nothing happened after Ghouta. He used chemical weapons, he didn't fall and he's still there," he said, referring to Syrian President Bashar al-Assad. "The fact the international community did nothing has encouraged him and encouraged Islamic State to do the same."

UN confirms previous chlorine attacks

The Assad regime has been repeatedly accused of using chlorine gas as a chemical weapon, and a UN investigation in August found that regime forces had twice carried out chlorine attacks.

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Syria and its ally Russia have accused Islamist militants of using chlorine in the past. UN investigators also said last month it had found that ISIS had used mustard gas in the battlefield.

"The systematic use of chemical weapons in Syria with impunity for perpetrators has become the 'new normal,'" the Syrian American Medical Society said in a statement Tuesday.

Aleppo, prewar Syria's largest city and commercial hub, has been divided for years into areas under rebel and regime control. The city has been heavily hit by intensifying violence in recent months following the failure of an American- and Russian-brokered "cessation of hostilities."</s>The US-based Syrian American Medical Society, which supports one of three hospitals in Aleppo where the victims were taken, said one person was killed by the barrel bombs dropped during the alleged chemical attack on the Sukkari neighborhood Tuesday.

At least 37 children and ten women were among those hospitalized, the Aleppo Free Doctors Committee said.

The victims were struggling to breathe, coughing harshly and had the smell of chlorine on their clothes, the Aleppo Free Doctor's Committee said.

Most were discharged after several hours, but ten people remained in intensive care, including a pregnant woman in her last trimester whose unborn child was showing a weak pulse, the committee claimed. CNN cannot confirm the authenticity of the reports.

Harrowing footage distributed by the Syrian Civil Defense -- also known as the White Helmets -- showed young children and other victims being rushed to the hospital in the arms of rescuers, gasping desperately for air as they are given oxygen masks. Footage purporting to be of the blast site moments after the attack showed barrels lying on top of what's left of destroyed buildings. The video also shows a boy being washed with a hose by rescuers after being pulled from the rubble as the sirens of ambulances wail around him. Another video by the Aleppo Media Center shows a man laying almost lifeless at the same hospital as medics try to pump oxygen into his lungs. The UK-based Syrian Observatory for Human Rights also reported the attack, saying that medical sources accused regime warplanes of pounding the Sukkari neighborhood with barrel bombs "laden with poison gas." The Syrian government has denied using chlorine gas for military purposes in the past. Syrian President Bashar al-Assad was stripped of the majority of his chemical arsenal in 2013 after the U.S. threatened an attack due to their alleged use in the Damascus suburb of Ghouta, leading to a multinational deal under which the weapons were removed. However the deal did not remove stocks of chlorine, a dual-use chemical which has industrial applications, but can also be used as a crude chemical weapon, delivered by improvised barrel bomb. What happens when chlorine is used as a chemical weapon? Chlorine, element 17 on the periodic table, is a so-called dual-use chemical with a number of industrial uses. Fatal in high concentrations and harmful in lower doses, chlorine gas can also be used as a crude weapon. The chemical was widely used in the First World War. When inhaled, it reacts with water in the body to produce corrosive hydrochloric acid that damages human cells. The effects can begin within seconds to minutes, causing victims to experience difficulty breathing, chest tightness, coughing and eye and skin irritation. Inhaling high levels of chlorine can cause pulmonary edema -- when fluid builds up in the lungs. In conflict situations, delivery methods include dropping chlorine gas onto civilian areas from aircraft via improvised barrel bombs. The Assad regime has been repeatedly accused of using chlorine gas as a chemical weapon, and a UN investigation determined in late August found that regime forces had twice carried out chlorine attacks. Secretary of State John Kerry said last year that he was "absolutely certain" that the Syrian government had attacked its own people with chlorine -- an accusation the Syrian regime has denied. Syria and its ally Russia have accused Islamist militants of using chlorine in the past. UN investigators also said last month that it had found that ISIS had used mustard gas in the battlefield. CNN's Clarissa Ward: 'There are no winners in Aleppo' This still from a video shows a girl treated at a makeshift hospital after what a rescue group called a chemical attack on her Aleppo neighborhood. "The systematic use of chemical weapons in Syria with impunity for perpetrators has become the 'new normal,'" the Syrian American Medial Society said in a statement Tuesday. Aleppo, pre-war Syria's largest city and commercial hub, has been divided for years into areas under rebel and regime control. The city has been heavily hit by intensifying violence in recent months following the failure of a American- and Russian-brokered "cessation of hostilities" earlier this year.</s>BEIRUT -- The Syrian government dropped a bomb containing chlorine on a besieged neighborhood in the city of Aleppo on Tuesday, according to residents and hospitals in the area.

The reports could not be independently verified, and it was not clear how it was determined that chlorine gas was released.

A medical report from the al-Quds hospital in the besieged eastern rebel-held part of Aleppo was shared with journalists via text messages. It said at least 71 people, including 37 children and 10 women, were treated for breathing difficulties and dry cough, and that "a strong smell of chlorine emanated from their clothes." The report said 10 of the patients were in critical care, including a pregnant woman.

Ibrahem Alhaj, a member of the Syria Civil Defense first responders' team, also known as the White Helmets, said he got to the scene in the crowded al-Sukkari neighborhood shortly after a helicopter dropped barrels containing what he said were four chlorine cylinders. He said he himself had difficulty breathing and used a mask soaked in saltwater to prevent irritation.

At least 80 civilians were taken to hospitals and treated for breathing difficulties, he said. A video by the rescuers shows children crying and men coughing.

"Most of those injured where women and children," he said in a telephone interview. "It is a crowded neighborhood."

The head of the Britain-based Syrian Observatory for Human Rights said 70 people suffered from breathing difficulties after the barrel bomb attack in al-Sukkari. The Observatory's chief, Rami Abdurrahman, said he could not ascertain whether it was chlorine gas attack.

Chlorine gas is a crude weapon that can be fatal in high concentrations. In lower doses, it can damage lungs or cause severe breathing difficulties and other symptoms, including causing a person to throw up and experience nausea.

The attack came as Syrian government loyalists battled to consolidate their hold over what had been the last rebel supply line into the opposition-held east of the city, after the capture of the route on Sunday.

Witnesses in Aleppo said the chlorine was apparently contained in a barrel bomb dropped on the al-Sukkari neighborhood on Tuesday afternoon. Aref al-Aref, a resident and activist, said he rushed to the area as soon as he heard the explosion and found people prostrate on the ground, without immediate evidence of injuries.

"There was no trace of shrapnel or gaping wounds or anything like that, which I thought was odd," he said. "They were just coughing intensely and having trouble breathing, and there was this smell as if a swimming pool had exploded in the area."

The use of chlorine as a weapon of war is banned under international conventions.

A team of international inspectors determined in late August that the Syrian government and Islamic State militants were responsible for chemical attacks carried out in 2014 and 2015. But the U.N. Security Council failed to agree on whether to impose sanctions on the government in line with a September 2013 resolution authorizing sanctions that can be militarily enforced for any use of chemical weapons in Syria.

This was the second reported chlorine attack in a month in rebel-held Aleppo, and though chlorine attacks kill fewer people than the conventional bombings that claim dozens of lives on a daily basis, they deepen the fears of people trapped by the war.

"I saw the horror of all the people. Everyone was scared," said Abdulkafi Hamdo, an Aleppo activist who arrived in the area shortly after the attack. "They were shocked. They don't know what to do. 'It's chlorine,' they were saying. 'What will they use after this?'"

U.S.-Russian negotiations have focused on securing a cease-fire around Aleppo and the delivery of humanitarian aid to civilians along the route that was captured by the government on Sunday.

A Turkish spokesman said Turkey was pushing for the cease-fire, which would extend through the Muslim religious holiday of Eid al-Adha, due to begin Monday.

Spokesman Ibrahim Kalin said President Recep Tayyip Erdogan spoke to his U.S. and Russian counterparts during the Group of 20 meeting in China about the cease-fire.

Kalin told private broadcaster NTV on Tuesday that the initial plan was for a 48-hour ceasefire.

U.S. officials have said they plan to keep talking to Russia and are still hopeful they can secure a deal. But now that the Syrian government has succeeded in surrounding Aleppo entirely, it is unclear whether the forces loyal to Assad would be prepared to accept terms that would impede their ability to continue to attack the rebels, even if the United States and Russia were to agree.

Also Tuesday, the Turkish government said two Turkish soldiers were killed and five were injured in an attack by the Islamic State on two Turkish tanks in northern Syria.

They were the first casualties inflicted by the Islamic State since Turkey dispatched troops and tanks to the area recently.

Information for this article was contributed by Liz Sly of The Washington Post and by Sarah El Deeb and Zeynep Bilginsoy of The Associated Press.</s>Syrian activists and rescue workers in the rebel-held part of the contested city of Aleppo said that government warplanes dropped suspected chlorine bombs Tuesday on a crowded neighborhood, injuring dozens.

The report could not be independently verified and it was not clear how it was determined that chlorine gas was released.

Accusations involving use of chlorine and other poisonous gases are not uncommon in Syria's civil war, and both sides have denied using them while blaming the other for using it as a weapon of war. Last month, there were at least two reports of suspected chlorine attacks in Aleppo also, while the Syrian government also blamed the opposition for using the gas.

In Tuesday's attack, a medical report from one of the hospitals in the besieged eastern rebel-held part of Aleppo was shared with journalists via text messages. It said at least 71 persons, including 37 children and 10 women, were treated for breathing difficulties, dry cough, and that their clothes smelled of chlorine. The report said 10 of the patients are in critical care, including a pregnant woman.

Ibrahem Alhaj, a member of the Syria Civil Defense first responders' team, said he got to the scene in the crowded al-Sukkari neighborhood shortly after a helicopter dropped barrels containing what he said were four chlorine cylinders. He said he himself had difficulty breathing and used a mask soaked in salt water to prevent irritation.

At least 80 civilians were taken to hospitals and treated for breathing difficulties, he said. A video by the rescuers shows children crying and men coughing.

"Most of those injured where women and children," he told The Associated Press in a telephone interview. "It is a crowded neighborhood."

The head of the Britain-based Syrian Observatory for Human Rights said 70 people suffered from breathing difficulties after a barrel bomb attack in al-Sukkari on Tuesday. The Observatory's chief, Rami Abdurrahman, said he could not ascertain if it was chlorine gas attack.

Chlorine gas is a crude weapon that can be fatal in high concentrations. In lower doses, it can damage lungs or cause severe breathing difficulties and other symptoms, including vomiting and nausea.

A team of international inspectors determined in late August that the Syrian government and Islamic State militants were responsible for chemical attacks carried out in 2014 and 2015. But the U.N. Security Council failed to agree on whether to impose sanctions on the government in line with a September 2013 resolution authorizing sanctions that can be militarily enforced for any use of chemical weapons in Syria.

The resolution followed Syria's approval of a Russian proposal to relinquish its chemical weapons stockpile and join the Chemical Weapons Convention. That averted a U.S. military strike in response to an alleged chemical weapons attack that killed hundreds in the Damascus suburb of Ghouta.

Fighting in the deeply contested city of Aleppo has not let up despite international efforts to establish a cease-fire. On Sunday, Syrian pro-government forces backed by airstrikes launched a wide offensive in the city, capturing areas they lost last month and besieging rebel-held neighborhoods once more after a breach in the siege a month earlier.

On Tuesday, a Turkish spokesman said Turkey was pushing for a ceasefire in Aleppo that would extend through the Muslim religious holiday of Eid al-Adha, due to begin Monday. Spokesman Ibrahim Kalin said President Recep Tayyip Erdogan spoke to his U.S. and Russian counterparts during the G20 meeting in China about the ceasefire.

Kalin told private broadcaster NTV Tuesday that the initial plan was for a 48-hour ceasefire.

Erdogan also repeated calls for a safe-zone to be established between the Syrian towns of Azaz and Jarablus in Aleppo province, to protect civilians. Turkey has pushed for a safe zone in Syria since at least 2014.

Turkey sent tanks into Syria last month to support rebel forces against the Islamic State group in the town of Jarablus. It expanded its operation into nearby al-Rai over the weekend.</s>This story contains graphic images, including some of child victims.

(CNN) Fresh airstrikes rained down Wednesday on a rebel-held neighborhood in Syria's east Aleppo, killing two people at a market where an alleged chlorine gas attack injured more than 100 people a day earlier, an activist told CNN.

The two at the market were among at least seven people killed and 40 injured in the latest strikes on the Sukkari neighborhood, the activist with the Aleppo Media Center said. The center is a group of opposition-affiliated activists documenting the conflict in the city.

In Tuesday's alleged chemical attack, more than 100 people -- including dozens of children -- were admitted to the hospital after barrels suspected of containing chlorine gas were dropped, medical group activists say.

Wednesday's airstrikes struck the market, a mosque, a street and a roundabout in the rebel-occupied neighborhood, the activist said.

He described scenes of terror at the market as he arrived in the aftermath.

"People were very afraid," he said. He told of a boy and a girl crying as they searched for their father, a sandwich seller, and emergency vehicles speeding in fear of further strikes from military jets overhead.

There were desperate scenes at a hospital where a team of two doctors and two nurses tended to people's injuries.

"It was another massacre," the activist said.

Chlorine gas allegedly was dropped about 1 p.m. local time Tuesday in barrel bombs from a helicopter, according to another Aleppo Media Center activist who attended the aftermath of the blast. 

The drop was followed by four rockets fired by military jets, he said.

"When I arrived at the market, I started seeing the injured people and noticed that something was unusual," he said.

"The injured did not have any signs of injuries or blood," he said, but instead were coughing loudly and had red, teary eyes.

"From 300 meters from the center of the barrel bomb, I started smelling chlorine, and I realized it was a chlorine bomb," he said.

At least 37 children and 10 women were among those hospitalized, the Aleppo Free Doctors Committee said in a statement.

The victims were struggling to breathe, coughing harshly, and they had the smell of chlorine on their clothes, the statement said.

Most were discharged after several hours, but 10 people remained in intensive care, including a pregnant woman in her last trimester whose unborn child was showing a weak pulse, the committee said.

CNN cannot confirm the authenticity of these reports.

Harrowing footage distributed by the Syrian Civil Defense -- a volunteer group also known as the White Helmets -- showed young children and others being rushed to the hospital in the arms of rescuers, gasping desperately for air while being given oxygen masks.

Footage purporting to be of the blast site moments afterward showed barrels lying on top of what's left of destroyed buildings.

In the video, rescuers washed a boy with a hose after he was pulled from the rubble as sirens wail around him.

The UK-based Syrian Observatory for Human Rights also reported the attack, saying that medical sources accused regime warplanes of pounding the Sukkari neighborhood with barrel bombs "laden with poison gas."

Hamish de Bretton-Gordon, a chemical weapons expert who is an adviser to nongovernmental organizations in Syria and Iraq, said chlorine gas could be deadly, and was a powerful psychological weapon.

The use of the widely available chemical in warfare was a war crime, he said.

"It's not nearly as toxic as nerve agents like sarin. It's a choking agent, and if you breathe enough of it, it creates hydrochloric acid," he said.

"Children's lungs are much more susceptible. That's one of the reasons you see much more child casualties than adults."

He said the Syrian conflict has seen a resurgence in chemical weapons, which had not been widely used since the Iran-Iraq War and Saddam Hussein's campaign against the Kurds in the late 1980s.

The international community took no military action in response, although a multinational deal was struck under which the majority of Syria's chemical arsenal was removed.

However, the deal did not remove stocks of chlorine, a dual-use chemical that has industrial applications but can also be used as a crude chemical weapon, delivered by improvised barrel bomb.

"The barrel bombs are basically liquid cylinders of chlorine that they throw out a helicopter," de Bretton-Gordon said.

"You don't even need a very big explosive -- just enough to split the barrel."

Since the Ghouta attack, he estimated that chemical weapons had been used more than 100 times in the conflict, and their effectiveness when deployed by the regime against ISIS had encouraged the terror group to use them in turn.

"Nothing happened after Ghouta. He used chemical weapons, he didn't fall and he's still there," he said, referring to Syrian President Bashar al-Assad. "The fact the international community did nothing has encouraged him and encouraged Islamic State to do the same."

Syria and its ally Russia have accused Islamist militants of using chlorine in the past. UN investigators also said last month it had found that ISIS had used mustard gas in the battlefield.

"The systematic use of chemical weapons in Syria with impunity for perpetrators has become the 'new normal,'" the Syrian American Medical Society said in a statement Tuesday.

Aleppo, prewar Syria's largest city and commercial hub, has been divided for years into areas under rebel and regime control. The city has been heavily hit by intensifying violence in recent months following the failure of an American- and Russian-brokered "cessation of hostilities."</s>BEIRUT (AP) — Syrian activists and rescue workers in the rebel-held part of the contested city of Aleppo are saying that government warplanes have dropped suspected chlorine bombs on a crowded neighborhood, injuring dozens.

Ibrahem Alhaj, a member of the Syria Civil Defense first responders team, says he got to the scene of the suspected chlorine attack shortly after a helicopter dropped barrels containing what he said were four chlorine cylinders.

He says the cylinders fell in the crowded al-Sukkari neighborhood on Tuesday and that at least 80 civilians were transported to hospitals and treated for breathing difficulties. A video by the rescuers shows children crying and men coughing.

The report could not be independently verified and it was not clear how the activists determined that chlorine gas was released.</s>(CNN) Medical groups and activists in Syria frequently allege that the Assad regime uses chlorine gas in barrel bombs against rebel-held areas . Those claims have been supported by the United Nations and international human rights groups that have studied chemical attacks in Syria.

But why would the regime of Syrian President Bashar al-Assad -- which is backed by Russian air power and has an extensive conventional arsenal -- turn to such crude and outlawed weapons?

The answer, to many analysts, is simple: to spread terror among the civilian populations in rebel-held areas such as Aleppo and Idlib, to drive them from their homes and neighborhoods.

Chlorine barrel bombs are cheap to manufacture and simple to deliver. The gas is contained in cylinders inside the barrels, which are dropped from helicopters and burst on impact. Witnesses have reported finding containers "typically used for refrigerants in refrigerators and air-conditioners," according to Human Rights Watch

To experts such as Dr. Zaher Sahloul of the Syrian American Medical Society , the weapons are a crude but brutally effective way to spread fear. They are the "poor man's chemical weapon."

Sahloul visited the town of Sarmin in Idlib last year soon after an attack that bore all the hallmarks of chlorine use. Many people had already left the area, terrified of another attack. Often, Sahloul told CNN, the chlorine barrel bombs would be dropped at night. Residents would hear a helicopter approach but there would be no explosion, just a creeping and intensifying vapor.

Barrel bombs containing chlorine don't kill large numbers of people. A United Nations envoy said about 400,000 people have been killed in the five-year conflict, but according to human rights groups, scarcely 1,500 of them have been killed by chemical weapons, and the majority of those casualties were inflicted by the use of sarin gas near Damascus in 2013. But chlorine bombs do spread panic and overwhelm medical facilities.

For parents, the horror and the threat it might be repeated the next night is enough to make them flee.

The effects of chlorine persist long after the attack, according to SAMS, which has documented dozens of chemical attacks in Syria. "Exposure victims and medical personnel often suffer from post-traumatic stress disorder, flashbacks and depression," SAMS said.

Sahloul said he believes the use of chemical weapons is part of a strategy to displace Syrians in opposition-held territories. Others suggest chlorine barrel-bombs are sometimes used as punishment in areas where regime forces are under attack. Human Rights Watch observed that a sequence of alleged chlorine attacks in Idlib province in March last year coincided with a major and ultimately successful rebel push to capture the capital of the province.

When the Assad regime agreed to surrender its chemical weapons stocks in 2013, chlorine was not on the list, in part because it's a widely used industrial chemical. But its use as a weapon is explicitly banned by the international Chemical Weapons Convention, which Syria has ratified.

The Syrian regime has repeatedly denied the use of chlorine, but a UN inquiry concluded last month after a yearlong investigation that the government had used chlorine gas in attacks in Idlib province in 2014 and 2015. The White House subsequently said there was "irrefutable evidence" the regime had used weaponized chlorine.

Last year, Dr. Annie Sparrow, an assistant professor of global health at Mount Sinai Hospital in New York, told a congressional committee the regime's use of chlorine gas was "emblematic of its war-crime strategy."

Sparrow, who spent time working in northern Syria, said: "The Assad regime has transformed a principal element of public health into a tool of disease and terror."

"The regime has found very cheap ways to kill people and drive them from their homes," said Sahloul. "A barrel costs less than $200, and you can't ban the import of chlorine, which is used in water purification, for example."

Human rights groups said that despite UN Security Council resolutions, the use of chlorine-filled bombs has not been punished. In a way, Sahloul said, their continued use by the regime "is one way that it sticks its finger in the eyes of the international community."

For the regime, the potential gain -- driving civilians from opposition-held areas and leaving rebel groups exposed to attack -- is worth the price, he said.</s>Syrian government aircraft have dropped suspected chlorine bombs on a crowded district of Aleppo, injuring dozens, activists and rescue workers said.

The report could not be independently verified.

Accusations involving the use of chlorine and other poisonous gases are not uncommon in Syria’s civil war, and both sides have denied using them.

Last month, there were at least two reports of suspected chlorine attacks in Aleppo, while the Syrian government also blamed the opposition for using the gas.

In the latest attack, a medical report from one of the hospitals in the besieged eastern rebel-held part of Aleppo was shared with journalists.

It said at least 71 people including 37 children and 10 women were treated for breathing difficulties, dry cough, and that their clothes smelled of chlorine. The report said 10 of the patients are in critical care, including a pregnant woman.

Ibrahem Alhaj, a member of the Syria Civil Defence first responders’ team, said he got to the scene in the crowded al-Sukkari area shortly after a helicopter dropped barrels containing what he said were four chlorine cylinders.

He said he had difficulty breathing himself, and used a mask soaked in salt water to prevent irritation.

At least 80 civilians were taken to hospitals and treated for breathing difficulties, he said. A video by the rescuers shows children crying and men coughing.

“Most of those injured were women and children,” he said. “It is a crowded neighbourhood.”

The head of the Britain-based Syrian Observatory for Human Rights said 70 people suffered from breathing difficulties after a barrel bomb attack in al-Sukkari on Tuesday. The Observatory’s chief, Rami Abdurrahman, said he could not ascertain if it was chlorine gas attack.

Chlorine gas is a crude weapon that can be fatal in high concentrations. In lower doses, it can damage lungs or cause severe breathing difficulties and other symptoms, including vomiting and nausea.

A team of international inspectors determined in late August that the Syrian government and Islamic State militants were responsible for chemical attacks carried out in 2014 and 2015.

But the UN Security Council failed to agree on whether to impose sanctions on the government in line with a September 2013 resolution authorising sanctions that can be militarily enforced for any use of chemical weapons in Syria.

The resolution followed Syria’s approval of a Russian proposal to relinquish its chemical weapons stockpile and join the Chemical Weapons Convention. That averted a US military strike in response to an alleged chemical weapons attack that killed hundreds in the Damascus suburb of Ghouta.

Fighting in the deeply contested city of Aleppo has not let up despite international efforts to establish a ceasefire.

On Sunday, Syrian pro-government forces backed by air strikes launched a wide offensive in the city, capturing areas they lost last month and besieging rebel-held neighbourhoods once more after a breach in the siege a month earlier.

On Tuesday, a Turkish spokesman said Turkey was pushing for a ceasefire in Aleppo that would extend through the Muslim religious holiday of Eid al-Adha, due to begin on Monday. Spokesman Ibrahim Kalin said President Recep Tayyip Erdogan spoke to his US and Russian counterparts during the G20 meeting in China about the ceasefire.</s>Syrian government forces have been accused of dropping barrel bombs containing chlorine from helicopters on a suburb of Aleppo, injuring 80 people.

 Volunteer emergency workers say people suffered breathing difficulties after an attack on the Sukari area.

 The reports could not be independently verified. An UN-led investigation in August found the government had used chlorine on at least two occasions.

 The Syrian government has always denied using chemical weapons.

 Ibrahem Alhaj, a Syrian Civil Defence rescue worker, said he had reached the scene of the attack shortly after a helicopter dropped barrels containing what he said were four chlorine cylinders.

 Syrian civil defence, a volunteer emergency response team that operates in opposition-held areas, posted video on its Facebook page showing distressed children using oxygen masks to breathe.

 The group accused the government of another chlorine attack in August.

 Russia, an ally of the Syrian government, has accused rebels of firing shells containing ‘toxic gas’ at government-held areas in Aleppo.

 Chlorine is a common industrial chemical, but its use in weapons is banned by the Chemical Weapons Convention.

 The UN said on Tuesday that a brief period of relief early this year for civilians caught up in the war in Syria had been replaced by an even more brutal resumption in fighting.

 In its 12th report on Syria, it said the cessation of hostilities in February had allowed some towns to receive their first aid in years but it only lasted a few weeks.

 The report says 600,000 Syrians now live under siege with a further 300,000 trapped in the city of Aleppo.

 On Sunday, Syrian government forces were reported to have recaptured parts of Aleppo city which were lost to rebels last month, placing rebel-held districts in the city’s east once again under siege.

 Monitors said government troops had recaptured two military academy sites in the Ramouseh district south of the city and severed a recently established rebel supply line.</s>BEIRUT (Reuters) - A suspected chlorine gas attack on an opposition-held neighborhood in the Syrian city of Aleppo caused dozens of cases of suffocation on Tuesday, rescue workers and a monitoring group said.

The Syrian Civil Defense, a rescue workers’ organisation that operates in rebel-held areas, said government helicopters had dropped barrel bombs containing chlorine on the Sukari neighborhood in eastern Aleppo.

The Syrian government has denied previous accusations it used chemical weapons during the five-year-old civil war. The Syrian army could not be immediately reached for comment on the latest allegations.

The Civil Defense said on its social media page that 80 people had suffocated. It reported no deaths. It posted a video showing wheezing children doused in water using oxygen masks to breathe.

The British-based Syrian Observatory for Human Rights, which tracks Syrian violence using sources on the ground, said medical sources had reported 70 cases of suffocation.

A United Nations and Organization for the Prohibition of Chemical Weapons inquiry seen by Reuters last month found that Syrian government forces were responsible for two toxic gas attacks in 2014 and 2015 involving chlorine.

The Civil Defense accused the government of two other suspected chlorine gas attacks in August . The United Nations Commission of Inquiry on Syria said it was investigating an August incident.

“Unimaginable crimes are occurring in Aleppo … pro-government aerial bombardments cause mass civilian casualties,” Commission Chairman Paulo Pinheiro told reporters in Geneva. “In government-held areas, indiscriminate ground shelling (by) armed groups … is also killing scores of civilians,” he added.

Aleppo has been one of the areas hardest hit by escalating violence in recent months after the collapse of a partial truce brokered by the United States and Russia in February.

Government forces put eastern Aleppo under siege on Sunday for a second time since July after advancing against terrorists on the city’s outskirts. The city has long been divided between government and opposition areas of control.

The Syrian conflict has killed more than 250,000 people and forced more than 11 million from their homes.
A chlorine attack in Aleppo on Tuesday injures more than 100 people. The blast from barrel bombs dropped kills one person.