Media playback is unsupported on your device Media caption "Bodies lying on the side of the road, children among them" - BBC Arab affairs editor Sebastian Usher

A huge car bomb has blasted a convoy of coaches carrying evacuees from besieged government-held towns in Syria, killing about 75 people, state media said.

It shattered coaches and set cars on fire, leaving a trail of bodies including children, as the convoy waited in rebel territory near Aleppo.

There were fears of revenge attacks on evacuees from rebel-held towns, being moved under a deal.

But the exchange later resumed, with coaches reaching safety on both sides.

The "Four Towns" deal brokered by Iran and Qatar was meant to relieve suffering in besieged towns - Foah and Kefraya in the north-west which are under government control, and rebel-held Madaya and Zabadani, near Damascus.

Some 20,000 besieged people would be taken out in all. According to AFP news agency, up to 5,000 government evacuees and 2,200 from rebel towns had been stranded in transit on Sunday.

Last month, the UN described the situation in the besieged towns as "catastrophic". More than 64,000 civilians are "trapped in a cycle of daily violence and deprivation", it said.

What do we know of the bombing?

The bomb reportedly went off at Rashidin, west of government-held Aleppo, at around 15:30 local time (12:30 GMT) at the checkpoint where the handover was due to take place.

Image copyright EPA Image caption Injured survivors were taken to hospital in Aleppo

A suicide bomber driving a van supposedly carrying aid supplies blew it up near the coaches, the UK-based Syrian Observatory for Human Rights reports.

"A van was distributing crisps," one civilian evacuee told Zaman English News. "Children started running after it. It then exploded."

At least 45 body bags were counted at the scene of the blast, while White Helmets rescuers, who operate in rebel-held areas, said at least 100 people had been killed. Many were also injured.

Images from the scene show bodies lying on the ground outside blackened and devastated vehicles.

Most of the dead were evacuees but they also included several rebels who had been guarding the buses, the Observatory says.

Convoys on both sides had been held up overnight, but by Saturday evening 15 coaches from the government towns had arrived at their destination in Ramouseh while between 25 and 30 carrying evacuees from the rebel towns had reached Rashidin.

Rebels had accused the government of breaching the terms of the deal, accusing it of trying to bring out more loyalist fighters than agreed, along with civilians.

Image copyright Reuters Image caption Government evacuees had been waiting under rebel guard when the bomb went off

Where does this leave the rebel evacuees?

According to a 24Aleppo tweet, a special unit of the Russian army surrounded the convoy from the rebel-held towns after the bombing and closed the road there to "prevent any reaction".

Image copyright AFP Image caption The rebel evacuees arrived near Aleppo on Friday

Evacuees from Madaya heard the blast from a bus garage where they had been waiting in Ramouseh, just a few miles away, Reuters news agency reports.

They called on international organisations to protect them from any possible retaliation, saying they condemned the attack on the other convoy.

Madaya resident Ahmed, 24, told Reuters earlier that evacuees had been waiting without drinking water or food at a since Friday night.

The Madaya and Zabadani evacuees are going to rebel-held territory in Idlib province.

Why are the evacuations needed?

Many people are reported to have died as a result of shortages of food or medicine in the four towns.

Foah and Kefraya, most of whose residents are Shia Muslims, have been encircled by rebels and al Qaeda-linked Sunni Muslim jihadists since March 2015.

Madaya and Zabadani, which are predominantly Sunni Muslim, have been besieged since June 2015 by the Syrian army and fighters from Lebanon's Shia Muslim Hezbollah movement.

A previous attempt at mutual evacuations failed in December when rebels burnt coaches due to be sent to the towns.

How desperate is Syria's war?

More than 300,000 people have lost their lives and millions of people have been displaced since a peaceful uprising against President Bashar al-Assad six years ago turned into a full-scale civil war.

More than 80 people were killed in a suspected chemical attack on the rebel-held town of Khan Sheikhoun, in the north-west, on 4 April, prompting the US to bomb a government air base with missiles.

Russia and Iran also have military forces deployed in the country, backing President Assad.

Rescue workers from both the government and rebel sides worked at the scene of Saturday's attack.

"Today, rebels and regime, Sunnis and Shias shed blood, sweat and tears together to save #Syria children," tweeted BBC producer Riam Dalati. "Maybe not all is lost, yet."</s>About 100 people were killed Saturday in a car bomb explosion targeting pro-regime evacuees leaving besieged Syrian towns, a volunteer rescue agency said.

The blast, which struck buses of people who were leaving their towns as part of a rebel-regime swap, also injured 55 others in Rashidin, a suburb of Aleppo in northwestern Syria, according to Syria Civil Defense, also known the White Helmets

The convoy of buses, which were parked at the time, was carrying thousands of people from two regime-held but rebel-besieged villages in northwestern Syria, state-run media reported.

Video shown on Syrian state-run television showed heavily damaged and burned buses parked on the side of a road. People walked outside the buses, surveying the damage as well as bodies lying on the roadway and a grass median.

The evacuees, from the mainly pro-regime Shia villages of Al-Fu’ah and Kafriya, were bound for regime-held parts of Aleppo.

They had been allowed to leave their villages this week as part of a Shia-Sunni exchange agreement between the Syrian government and insurgents who have been fighting a civil war for six years.

As part of the deal, government forces are allowing thousands of rebels and civilians to leave two towns in southwest Syria: Madaya and Zabadani, according to the London-based Syrian Observatory for Human Rights.

Madaya and Zabadani have been under the control of anti-government fighters but facing siege from forces loyal to the regime.

The explosion happened as both sets of evacuees were stopped in separate locations outside Aleppo. Each were heading to areas controlled by forces friendly to them.

The explosives-rigged car had been packed with children’s food supplies, perhaps to disguise it, a correspondent with the state-run Syrian Arab News Agency reported.

The convoy that departed Al-Fu’ah and Kafriya is carrying 5,000 people, the Syrian Observatory for Human Rights said.

Thousands were leaving Madaya and Zabadani, including more than 2,000 rebel fighters, their families and other civilians, the monitoring group said.

The deal was brokered by Iran and Qatar, Agence France-Presse reported.</s>The blast, which struck buses of people who were leaving their towns as part of a rebel-regime swap, also injured 55 others in Rashidin, a suburb of Aleppo in northwestern Syria, according to Syria Civil Defense, also known the White Helmets.

The convoy of buses, which were parked at the time, was carrying thousands of people from two regime-held but rebel-besieged villages in northwestern Syria, state-run media reported. Video shown on Syrian state-run television showed heavily damaged and burned buses parked on the side of a road. People walked outside the buses, surveying the damage as well as bodies lying on the roadway and a grass median.

The evacuees, from the mainly pro-regime Shia villages of Al-Fu’ah and Kafriya, were bound for regime-held parts of Aleppo. The state-run Syrian Arab News Agency reported the convoy continued, and the first buses arrived late Saturday in Aleppo. The buses headed to the Jebrin area for a temporary housing center equipped with food and medical supplies, SANA said. The rebel group Ahrar al-Sham tweeted that some of its members died in the blast. They were at the site to ensure the convoy’s passage, Ahrar al-Sham said. The group said it was investigating to find out who was responsible. The evacuees had been allowed to leave their villages this week as part of a Shia-Sunni exchange agreement between the Syrian government and insurgents who have been fighting a civil war for six years. As part of the deal, government forces are allowing thousands of rebels and civilians to leave two towns in southwest Syria: Madaya and Zabadani, according to the London-based Syrian Observatory for Human Rights. Madaya and Zabadani have been under the control of anti-government fighters but facing siege from forces loyal to the regime.

State-run media: Rigged car was disguised

 The explosion happened as both sets of evacuees were stopped in separate locations outside Aleppo. Each were heading to areas controlled by forces friendly to them.

The explosives-rigged car had been packed with children’s food supplies, perhaps to disguise it, a correspondent with SANA reported.

The convoy that departed Al-Fu’ah and Kafriya is carrying 5,000 people, the Syrian Observatory for Human Rights said.

Thousands were leaving Madaya and Zabadani, including more than 2,000 rebel fighters, their families and other civilians, the monitoring group said.

The deal was brokered by Iran and Qatar, Agence France-Presse reported.</s>SYRIA — The death toll from a bomb explosion targeting evacuees leaving besieged Syrian towns has gone up to 112, a monitoring group said Sunday.

The blast hit a convoy of buses Saturday, according to the Syrian Observatory for Human Rights, which reported the higher death toll.

The blast struck buses of people leaving their towns as part of a rebel-regime swap. In addition to the deaths, it also injured 55 others in Rashidin, a suburb of Aleppo, according to Syria Civil Defense, also known as the White Helmets

The convoy of buses, which were parked at the time, was carrying thousands of people from two regime-held but rebel-besieged villages in northwestern Syria, state-run media reported.

People were evacuating two rebel-held towns in southwest Syria at the same time under a so-called Four Towns Agreement.

Video shown on state television showed charred buses parked on the side of a road. People walked outside the buses, surveying the damage as well as bodies lying on the roadway and a grass median.

The evacuees, from the mainly pro-regime Shia villages of Al-Fu’ah and Kafriya, were bound for regime-held parts of Aleppo.

The state-run Syrian Arab News Agency reported the convoy continued, and the first buses arrived late Saturday in Aleppo. The buses headed to the Jebrin area for a temporary housing center equipped with food and medical supplies, SANA said.

During a televised interview, Rami Abdul Rahman, director of the Syrian Observatory for Human Rights, said a suicide bomber claimed he was carrying food items and blew himself up in a fuel station.

Abdul Rahman said he doesn’t believe the Syrian regime is behind the attack. He said the regime kills scores of people daily using all types of weaponry and doesn’t need to kill its own sympathizers.

The evacuees had been allowed to leave their villages this week as part of a Shia-Sunni exchange agreement between Syria and insurgents who have been fighting a civil war for six years.

As part of the deal, government forces are allowing thousands of rebels and civilians to leave two towns in southwest Syria: Madaya and Zabadani, according to the London-based Syrian Observatory for Human Rights.

Madaya and Zabadani have been under the control of anti-government fighters but facing siege from forces loyal to the regime.

The rebel group Ahrar al-Sham tweeted that some of its members died in the blast. They were at the site to ensure the convoy’s passage, Ahrar al-Sham said. The group said it was investigating to find out who was responsible.

The explosion happened as both sets of evacuees were stopped in separate locations outside Aleppo. Each were heading to areas controlled by forces friendly to them.

The explosives-rigged car had been packed with children’s food supplies, perhaps to disguise it, a correspondent with SANA reported.

The convoy that departed Al-Fu’ah and Kafriya had 5,000 people, the Syrian Observatory for Human Rights said.

Thousands were leaving Madaya and Zabadani, including more than 2,000 rebel fighters, their families and other civilians, the monitoring group said.

The deal was brokered by Iran and Qatar, Agence France-Presse reported.

A statement from the spokesperson for the U.N. Secretary-General said: “The evacuations were being conducted in accordance with the agreement reached pursuant to the Four Towns agreement. …

“We call on the parties to ensure the safety and security of those waiting to be evacuated. Those responsible for today’s attack must be brought to justice.”

The Syrian American Medical Society said in a statement: “This forced displacement is a clear violation of international humanitarian law, and marks yet another sad chapter in the history of this crisis. The absence of the UN and international community from this process has left the civilian populations especially vulnerable, leading to horrific events such as what took place today.

“The UN must not abandon its role in protecting innocent civilians and enforcing international humanitarian laws.”</s>BEIRUT — At least 100 people were killed Saturday in an explosion that hit near buses carrying people evacuate from a besieged area of government loyalists, according to the Syrian opposition rescue service.

The explosion was caused by a car bomb, according to Syrian TV and the opposition Britain-based Syrian Observatory for Human Rights, who put the death toll earlier at 24 and said it would likely rise.

In footage aired on Syrian TV, bodies, including fighters, were seen lying alongside buses, some of which were charred and others gutted from the blast. Personal belongings could be seen dangling out of the windows. The state TV channel said the car was carrying food aid but a rebel spokesman said the car had been parked in the area and abandoned.

The explosion hit the Rashideen area, a rebel-controlled district outside Aleppo city where evacuation buses carrying nearly 5,000 people from the northern rebel-besieged villages of Foua and Kfraya were stuck, causing a huge plume of black smoke. Residents from the two villages had been evacuated Friday, along with more than 2,000 from Madaya, an opposition-held town outside of Damascus besieged by government forces.

A senior rebel leader said 20 fighters who guarded the buses were killed as well as dozens of passengers. He spoke on the condition of anonymity because he was not authorized to speak to the media. Yasser Abdellatif, a member of the powerful Ahrar al-Sham group which negotiated the deal, said at least 30 rebels were killed in the explosion.

The explosion came as frustration was already mounting over the stalling evacuation process. Thousands of evacuees from the pro-government and opposition areas were stuck opposite sides of the edge of Aleppo city as rebels and government bickered over the terms for evacuating fighters.

Prior to the blast, Syrian Red Crescent teams had distributed meals to the restless evacuees, stuck in limbo after having left their homes over 30 hours earlier. Many were already voicing their dissatisfaction with the wait.

“The people are restless and the situation is disastrous,” said Ahmed Afandar, a resident evacuated from his the opposition area near Madaya. “All these thousands of people are stuck in less than half a kilometre (500 yards).” He said the area was walled off from all sides and there were no restrooms.

Afandar said people were not allowed to leave the buses for a while before they were let out. Food was distributed after several hours and by early afternoon the evacuees from rebel-held areas were “pressured” to sit back on their buses, Afandar said.

“We are not moving forward or backward,” he said. The evacuees from Madaya were expected to head to rebel-held Idlib, west of Aleppo.

Syrian state TV blamed the rebels for obstructing the deal, causing thousands of evacuees to be stuck in bus depots overnight.

Salloum Salloum, a lawmaker speaking on the pro-government al-Ikhbariya TV channel, said efforts were underway to resolve the problem, accusing the rebels of adding new conditions to the deal.

An opposition representative, Ali Diab, told the pan-Arab Al-Arabiya TV that fewer armed men than agreed to were evacuated from the pro-government areas, violating the terms of the agreement.

A resident of Zabadani — another rebel-held town to be evacuated — Amer Burhan says no evacuation had even taken place from there.

The population transfer deal has been criticized by opponents as forced displacement and was not overseen by the United Nations.</s>A car bomb near Aleppo city targeted a convoy of buses carrying evacuees from two besieged towns, killing dozens of people, according to Syrian state media and rebels.

Those killed in Saturday’s attack included civilians and pro-regime fighters who had left their homes in the Idlib province towns of Fua and Kafraya, which had for years been besieged by opposition rebels. Rebel fighters who were escorting the convoy were also killed.

Initial casualty tolls varied. Syrian state media blamed the attack on “terrorists,” the term it uses to refer to armed rebels, saying they had targeted some of the 75 buses and 20 ambulances carrying evacuees. The dead included women and children, it said.

U.K.-based opposition monitor the Syrian Observatory for Human Rights said at least 43 people had been killed and dozens of others wounded.

A spokesman for Ahrar Al Sham, one of two rebel groups escorting the convoy, blamed the regime for the attack and said it had targeted the side of an exchange post where opposition fighters had lined up their vehicles.

An expanded version of this report appears at WSJ.com.</s>A car bomb exploded in Rashidin, west of Aleppo, killing dozens of evacuees, including children, that had been waiting on buses evacuating the Syrian towns of Foua (al-Fu’ah/Fuaa) and Kefraya (Kafriya). The evacuation was part of the “Four Towns” deal that the BBC reports was brokered by Iran and Qatar. Foua and Kefraya are besieged government-held towns, the BBC reports. Meanwhile, Madaya and Zabadani are besieged rebel-held towns, the BBC reports. Women and children were among those killed in the attack on the evacuation buses. The buses were filled with predominantly Shia civilians from the two pro-government Shia villages just trying to escape to safety.

Reuters reported that early Friday, civilians from “Shi’ite villages of al-Foua and Kefraya, besieged by rebel forces” left on buses headed for the government-held Aleppo. The buses arrived at the outskirts several hours later. While waiting to enter Aleppo, the buses were attacked.

The Syrian Observatory for Human Rights reportedly said the attack in Rashidin had specifically targeted residents evacuated from predominantly-Shia Foua and Kefraya. An AFP reporter in rebel-held Rashidin reported witnessing bodies, body parts, and blood. Children and other civilians, as well as pro-government fighters, were among those killed in the horrendous attack.

“The suicide bomber was driving a van supposedly carrying aid supplies and detonated near the buses,” the Observatory said.

State media said that the vehicle-borne improvised explosive device (VBIED) had been employed by “terrorist groups.” The Independent reported that the buses were being guarded by “al-Qaeda-linked alliance Hayat Tahrir al-Sham” fighters. Some fighters from that group were also killed in the VBIED explosion. Lebanese journalist Rana Harbi reported on Twitter that the explosion was set off by rebels, but other media outlets have yet to confirm who is responsible for the deaths of Shia civilians, including children.

Thousands of evacuees from the state-held towns of Foua and Kefraya waited in the streets. They had lived “under crippling siege for more than two years,” according to AFP. When the bomb exploded, they had been essentially sitting ducks, stuck on the road in Rashidin. A rebel source told AFP that the evacuees had been left stranded after disagreements came up pertaining to the number of loyalists fighters that were leaving.

“The blast hit the Rashidin area on the outskirts of Aleppo, where dozens of buses carrying mostly Shia Muslim families from pro-government villages were waiting to enter the city,” Lizzie Dearden, a reporter from The Independent, wrote, adding that the Shias had been predominantly targeted by ISIS “and to a lesser extent by al-Qaeda in the past.”

The victims of the blast from the pro-state villages that had reportedly experienced starvation under the siege, The Independent wrote.

“How can anyone trust the ‘rebels’? WE failed these children,” Lebanese journalist Rana Harbi wrote. “WE told them be patient. & after 2 years.. this? Burned in evacuation buses?”

The Cypress Weekly reported that the evacuees had been waiting in their buses to cross into government-held Aleppo. Many injured in the blast ended up entering the city in ambulances.

Dozens died in the blast, but exact numbers are still uncertain. A media unit run by Hezbollah, the Shiite Muslim political party and militant group, said the blast killed at least 40 people, Reuters reported. The Syrian Observatory for Human Rights said more than 24 people were killed, Reuters reported. Other reports indicate as many as 100 evacuees may have been killed in the bombing of the buses.

Journalist Rana Harbi shared extremely graphic images of the scene to her Twitter account, stating that she “can’t do this anymore.”

The images shared on social media depicting the aftermath of the detonation of the VBIED on a road in Rashidin outside of Aleppo may be disturbing to some readers.

Readers should use discretion scrolling down.

The following video and images contain extremely graphic visuals, including the actual deceased bodies of women and children evacuees from Foua and Kefraya, Syria, but have been shared on social media by concerned parties and journalists, reportedly so that the West might have a better idea of the nightmare of Syrian civilians’ lives.

Reporter Tobias Schneider said that evacuees from Zabadani and Madaya are terrified today of retribution against them because they make up the other side of the “Four Towns” evacuation deal.</s>At least 20 people have been killed in what is believed to have been a suicide car bomb attack targeting a convoy of evacuees waiting to enter Aleppo, according to reports.

A media unit run by Hezbollah, which backs the Syrian government of Bashar al-Assad, said the suspected attacker detonated a car bomb near the convoy of people evacuated from towns besieged by rebel forces in northern Syria.

An image shown on state TV showed a number of bodies on the floor and a huge plume of black smoke rising in the background.

A senior rebel official said 20 fighters guarding the buses had been killed, as well as dozens of passengers. Syrian state TV said 22 people had been killed. The UK-based Syrian Observatory for Human Rights put the figure at 24.

The convoy of nearly 5,000 people had been stuck in Rashidin on the outskirts of Aleppo after a population transfer deal with rebel forces stalled.

Under the agreement, more than 2,000 residents, activists and gunmen from areas besieged by government forces were also evacuated. Both groups, however, have been stuck in separate but adjacent areas while the two sides wrangle over the number of rebel fighters to be evacuated.

Before the blast, Syrian TV showed dozens of buses carrying thousands of people from the pro-government areas of Foua and Kafriya, and the opposition areas of Madaya and Zabadani, parked on the edge of Aleppo city, separated by walls.

Ahmed Afandar, a resident evacuated from his home near Madaya, said: “The people are restless and the situation is disastrous. All these thousands of people are stuck in less than half a kilometre.” The area was walled off on all sides and there were no toilets, he added.

The evacuees from Madaya were expected to head to rebel-held Idlib, 30 miles (48km) south-west of Aleppo. Afandar said people were not allowed to leave the buses for a while before they were let out.

Food was distributed after several hours and by early afternoon, the evacuees from rebel-held areas were “pressured” to sit back on their buses, Afandar said.</s>RASHIDIN - A powerful blast ripped through a bus convoy carrying evacuees near the Syrian city of Aleppo on Saturday, killing at least 100 people and injuring 48 others, according to state media and rescuers who responded to the scene.

Syrian state television said the convoy was hit by a suicide attacker with a car bomb. Pro-government activists claimed the vehicle used was a pick-up truck purporting to deliver food for the evacuees, LA Times reported.

Mohammad Taqi Din, the head of the crisis committee for the towns of Foua and Kefraya, said in a WhatsApp message on Saturday that the number of dead had risen to 40. No group has claimed responsibility for the attack.

Up to 5,000 evacuees had left a day earlier from Foua and Kefraya, a pair of Shiite-dominated towns in northwestern Syria, roughly 31 miles southwest of Aleppo, as part of a complex population swap brokered by Iran, Qatar and Turkey.

The towns had been encircled for years by a loose coalition of hard-line Islamist rebels, including the faction Ahrar al Sham as well as the former Al Qaeda affiliate Organization for the Liberation of Syria (once known as the Nusra Front).

Residents of Foua and Kefraya were joined by 2,350 others from Madaya, a rebel-held enclave that, along with the Damascene resort town Zabadani, had been besieged by pro-government forces, including the Lebanese paramilitary group Hezbollah.

The United Nations described the situation in the four towns as a “looming humanitarian catastrophe,” where tens of thousands of civilians were “trapped in a cycle of daily violence and deprivation.”

Officials brokered the “Four Towns Agreement,” which saw limited amounts of aid alleviate acute shortages of food and medicine, before a final evacuation was pushed through earlier this week.

Evacuees had been waiting for more than 24 hours in the Rashideen area, the last point of rebel control before government-held Aleppo. The Syrian Observatory for Human Rights, a pro-opposition monitoring group that tracks the carnage in the country, said there had been some objection by the rebel factions involved in the deal.

Mohammad Khair Hak, a pro-opposition cameraman who was at the gathering point of the buses, posted a video on his Facebook page purporting to show the aftermath of the blast.

The camera lingers on the first buses in the convoy, their right side completely obliterated by what Hak described as a “huge explosion.” On the ground are the remains of corpses partially hidden by a motley collection of brightly coloured blankets.

Somewhere in the distance a group of people shout “ambulance, ambulance,” while the camera captures the body of what appears to be a little boy hanging out the window of one of the buses.

Many fear that the attack will scuttle the evacuation agreement, which had taken months to negotiate. Thousands still remain in the four towns.

AFP adds: The Syrian Observatory for Human Rights said the vehicle exploded next to buses carrying residents evacuated from the northern towns of Fuaa and Kafraya under a deal reached between the regime and rebels.

The attack, in Rashidin, west of Aleppo, also wounded dozens, according to the Observatory and an AFP correspondent on the scene. "The suicide bomber was driving a van supposedly carrying aid supplies and detonated near the buses," the monitoring group said.

AFP's reporter in rebel-held Rashidin saw several bodies, body parts and blood scattered on the ground.

The bombing took place as thousands of evacuees from Fuaa and Kafraya waited to continue their journey to regime-controlled Aleppo, the coastal province of Latakia, or Damascus.

Syria's war has left more than 320,000 people dead since erupting in 2011, with more than half the population forced from their homes and hundreds of thousands enduring siege-like conditions. It has sucked in regional and international powers and allowed militant groups to seize vast areas of the country.

US-backed fighters reached the outskirts of a key militant-held town in northern Syria on Saturday as part of an offensive aimed at the IS bastion of Raqa.

The Syrian Democratic Forces (SDF), an Arab-Kurdish alliance supported by US-led coalition air strikes and special forces advisers, surrounded Tabqa in early April and have cut its main supply routes.

The town and a vast nearby dam are considered key prizes in the broader offensive for Raqa, the de facto Syrian capital of IS's self-proclaimed "caliphate", about 55 kilometres (34 miles) to the east.

An SDF military source said Saturday that clashes were "at their height" and that the alliance's forces were "trying to penetrate the town from the east and west".

The alliance was reported to have advanced overnight after driving the militants from two areas just southeast and southwest of the town.

SDF fighters are within a few hundred metres (yards) of Tabqa, said Observatory head Rami Abdel Rahman. He said heavy clashes were under way around the two suburbs as IS attempted to counter-attack. The SDF launched its campaign for Raqa in November and has since captured most of the surrounding province.

It has been backed by US-led coalition air strikes, along with advisers and even an American Marines artillery battery.

Raqa was home to around 240,000 residents before 2011 and more than 80,000 people have fled to the city from other parts of the country since the start of Syria's civil war.

Tabqa sits on a key supply route into Raqa and served as an important IS command base, housing the group's main prison.

Backed by Russia and local militias, pro-government forces have made a string of recent gains.

The government and rebels have brokered a series of deals to evacuate people from besieged areas, which Damascus touts as the best way to end the violence. Rebels say they are forced out by siege and bombardment.

The deal involving the evacuees targeted on Saturday has been beset by delays, and the 5,000 Fuaa and Kafraya residents had waited in Rashidin for more than a day without moving before the bomb went off, an AFP correspondent said.

Around 2,220 evacuees from Madaya and Zabadani were similarly blocked at a transit point in government-held territory, one of them told AFP by telephone.

State television said the car bombing had been carried out by "terrorist groups", a term the regime applies to all armed opposition groups.

A rebel official confirmed there had been disagreement over the number of opposition fighters allowed to leave Madaya and Zabadani.

Many residents had earlier expressed regret over not knowing when, if ever, they would be able to return to their homes. "It's terrible to be uprooted like this, to go and live in a place that is not ours," said Jama Nayef, a vet from Fuaa.</s>More than 100 people were killed in a car bomb blast in northern Syria on Saturday, when an explosion hit through the buses which were evacuating residents from two towns besieged by rebels, reports state.

The Syrian Observatory for Human Rights said that the blast was targeting buses which were carrying residents who were evacuated from the northern towns of Fuaa and Kafraya. The evacuation was reached under a deal between the Bashar al-Assad-led Syrian regime and rebels. The Syrian state television showed footage of burnt vehicles packed with people's luggage and bodies strewn across the ground.

Syria's six-year-long civil war between President Bashar al-Assad's regime and opposition rebels has left more than 320,000 people dead since 2011.

"The suicide bomber was driving a van supposedly carrying aid supplies and detonated near the buses," the monitoring group said, according to AFP reports. The human rights group also said that although most of the people who died in the explosion were evacuees, but the blast also killed several rebels who were guarding the buses in Rashidin, west of Aleppo.

The blast left thousands more evacuees stranded on the road over a disagreement on number of rebels allowed to leave other two towns which were included in the deal. The Observatory said that the evacuation process was resumed soon after the blast.

Reports state that several people were wounded in the incident, including women and children who were taken to a hospital in the government-held part of Aleppo for treatment.

The bombing was condemned by the rebel group Ahrar al-Sham, which said that they were securing the civilians at the time.

"We reject any accusations levelled at opposition for this heinous crime," a senior official tweeted. "Our role was to secure civilians not kill them."

More than 5,000 people who had been living under siege for more than two years, left the two towns on Friday. Reports state that around 2,200 people were also evacuated from rebel-held Madaya and Zabadani.
A car bomb strikes a convoy of buses near Aleppo which were carrying evacuees from the pro-government towns of Al-Fu'ah and Kafriya. Over 100 people are killed.