Media playback is unsupported on your device Media caption The BBC's Jeremy Bowen drives into west Aleppo ahead of the ceasefire 
 
 A cessation of hostilities has come into effect in Syria, although it is unclear how widely it will be observed. 
 
 The Syrian army says it is implementing the truce, which began at sunset, but rebel groups have been more guarded. 
 
 US Secretary of State John Kerry, who helped broker the deal, warned it could be the last chance for peace in a united Syria. 
 
 Humanitarian groups are hoping to make aid deliveries to the worst-hit areas, especially the war-torn city of Aleppo. 
 
 Mr Kerry, speaking at the state department in Washington, said early reports indicated "some reduction in violence". 
 
 But he said that it was too early to draw a definitive conclusion about how effective the truce would be. 
 
 Just after the ceasefire came into effect at sunset on Monday, the Syrian army announced a seven-day "freeze" on military operations. 
 
 The Syrian Observatory for Human Rights monitoring group reported that calm appeared to be prevailing on most front lines. 
 
 The deal was struck on Friday in Geneva after months of talks between Russia and the US. It also requires both sides to allow unhindered access for humanitarian aid to besieged areas. 
 
 Image copyright AP Image caption The Free Syrian Army has cautiously welcomed the cessation of hostilities 
 
 If the truce holds for seven days, the US and Russia will carry out co-ordinated air strikes on militant groups. 
 
 The opposition Free Syrian Army group has said that while it will "co-operate positively" with the ceasefire, it was concerned it would benefit the government. 
 
 Another major rebel group, the hardline Islamist Ahrar al-Sham, initially rejected the deal but later appeared to have softened its stance. 
 
 Opposition sources quoted by Reuters said a forthcoming statement supporting the cessation "with harsh reservations" would be backed by "the largest groups", including Ahrar al-Sham. 
 
 Media playback is unsupported on your device Media caption President Bashar al-Assad: "The Syrian state is determined to recover all areas from the terrorists" 
 
 Speaking earlier, President Bashar al-Assad welcomed the deal but said the Syrian state was still "determined to recover every area from the terrorists, and to rebuild". 
 
 The cessation of violence is due to be renewed every 48 hours. 
 
 Big test for US and Russia: BBC Middle East editor Jeremy Bowen 
 
 The strength, or otherwise, of the ceasefire is a big test of what appears to be a less sour, more workable relationship between the foreign ministers of the US and Russia. 
 
 Diplomacy failed in the first, critical years of the war. A major reason for that was diplomatic deadlock between President Bashar al-Assad's ally, Russia, and the US, which demanded his immediate departure from office. 
 
 Since then Russia has become the most influential outside power in Syria. The US and its Western allies have struggled to keep up. 
 
 Perhaps Moscow is now ready to build on a ceasefire, if it lasts, to push President Assad towards a political transition that might end the war. 
 
 Or perhaps, as enemies of President Assad and the Russians believe, the ceasefire will be a chance to regroup and rearm. 
 
 The truce followed a weekend of air strikes by government forces on several rebel areas that killed about 100 people. 
 
 Russian warplanes were also in action in the provinces of Idlib and Aleppo, say Syrian activists. 
 
 Image copyright Abo Anas Image caption Children play on a bomb in the al-Muyaser neighbourhood in Aleppo 
 
 Syrian children celebrate Eid in a warzone 
 
 Such intensification of violence has occurred before other, aborted, ceasefires in Syria. 
 
 Under the plan, Syrian government forces will halt combat missions in specified opposition-held areas. 
 
 Russia and the US will then establish a joint centre to combat jihadist groups, including so-called Islamic State and Jabhat Fateh al-Sham (known until recently as the Nusra Front). 
 
 The conflict in Syria, which began with an uprising against Mr Assad, has raged for five years and claimed the lives of more than a quarter of a million people. 
 
 More than 4.8 million have fled abroad, and an estimated 6.5 million others have been displaced within the country, the UN says. 
 
 If the truce holds... 
 
 Image copyright GEORGE OURFALIAN Image caption Government forces have regained ground in Aleppo 
 
 Jihadist groups like so-called Islamic State and Jabhat Fateh al-Sham face the joint might of the Russian and US air forces 
 
 Moderate rebels and civilians in the areas they hold will no longer face the threat of indiscriminate air strikes such as barrel-bombing although the Syrian air force will not be grounded completely; aid deliveries will be allowed to areas currently under siege 
 
 President Assad will be in a stronger position as the US and Russia engage two of his most effective military opponents while moderate rebels observe the truce with his forces 
 
 Syria's history of failed deals 
 
 Image copyright AFP Image caption Can Kerry (left) and Lavrov succeed at last? 
 
 February 2012: Syrian government "categorically rejects" an Arab League plan calling for a joint Arab-UN peacekeeping mission 
 
 June 2012/January 2014/January 2016: Three failed UN-sponsored peace conferences in Geneva 
 
 September 2013: Kerry and Lavrov negotiate a deal to strip the Syrian government of its chemical weapons in return for the US backing away from air strikes. Since then, the government has again and repeatedly been accused of using toxic chemicals against rebel-held areas 
 
 February 2016: World powers agree in Munich on a nationwide "cessation of hostilities" in Syria excluding jihadist groups. There is no agreement on any joint US-Russian operations. The "pause" quickly unravels as Assad promises to regain control of the whole country 
 
 March 2016: President Vladimir Putin declares "mission accomplished" in Syria and orders removal of "main part" of Russia's air army in Syria. Russian air strikes have continued ever since ||||| (CNN) As the sun set in Syria Monday, another ceasefire aimed at ending the country's bloody conflict began. Now the world watches with bated breath. 
 
 The country has faced an apparent intensification of airstrikes in the last 48 hours , a seemingly deliberate attempt by those on the ground to send a message of strength. 
 
 So will this agreement be a pivotal moment in the Syrian civil war or simply another brief hiatus in the death and destruction? Five questions about the latest truce: 
 
 How will it work? 
 
 The US and Russia brokered a pact to pause the violence on Friday after months of back and forth talks. US Secretary of State John Kerry, who negotiated the ceasefire along with his Russian counterpart Sergey Lavrov, said the deal would stop Syrian President Bashar al-Assad's air force from flying combat missions anywhere the opposition is present. 
 
 "That should put an end to the barrel bombs, an end to the indiscriminate bombing of civilian neighborhoods," Kerry said 
 
 The ceasefire will also allow for much-needed humanitarian access to besieged cities like Aleppo. 
 
 If the accords hold for seven days, Russia and the US will begin to discuss military options for targeting one-time al Qaeda affiliate Jabhat Fateh Al-Sham, previously known as the al Nusra Front , and ISIS. 
 
 Who does it apply to? 
 
 The deal is supposed to cover everyone involved in the fighting. But in reality that's difficult to enforce because there are so many groups in play. 
 
 The specifics of the agreement call for Assad's troops and the opposition to abide by the ceasefire. Terrorist groups, including ISIS and Jabhat Fateh Al-Sham, are not included in the agreement and military operations against them will continue. 
 
 Syria's opposition has said it welcomes the ceasefire but only "if it is going to be enforced," according to a statement form Bassma Kodmani, a member of the High Negotiations Committee on Saturday. 
 
 "When the cessation of hostilities was installed in February, the opposition -- 100 groups -- respected it. It was violated by the regime," Kodmani said. "So a return to a cessation of hostilities has been our demand." 
 
 The agreement has also been welcomed by the UN and foreign ministers from the UK, Turkey and Germany. 
 
 There is little trust between rebel groups and the regime itself. The rebels, for their part, agree to basic principles such as the creation of humanitarian corridors. But they have raised concerns about how the ceasefire will be monitored and what the consequences of any violations will be. There are also concerns that the deal will actually strengthen the regime and create a much more chaotic scene on the ground. 
 
 Will this push for peace be any different to previous attempts? 
 
 Nobody knows. 
 
 US Secretary of State Kerry stressed in the ceasefire announcement on Friday that this latest set of accords relies on the goodwill and trust of those involved. 
 
 "If the plan is implemented in good faith, if the stakeholders do the things that are available to them to do and are being called on to do, this can be a moment where the multilateral efforts at the diplomatic table, the negotiations could take hold, and you could really provide the people of Syria with a transition," he said. 
 
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 He also warned that the truce's success depends on Russia actually putting pressure on al-Assad. 
 
 "'We -- the Obama administration, the United States is going the extra mile here because we believe that Russia and my colleague have the capability to press the Assad regime to stop this conflict and to come to the table and make peace," he said. 
 
 This isn't the first time various parties have tried to end the bloody battles that have afflicted Syria since civil war broke out five years ago. 
 
 • In 2011, Syria signed an Arab League proposal aimed at stopping the fight between government forces and protestors but violence continued and the following month, the Arab League suspended its mission in the country. 
 
 • The UN has hosted three separate peace conferences in Geneva in hopes of ending the conflict, but each has ended without a breakthrough. 
 
 • The US and Russia coordinated a partial ceasefire back in February . But human rights groups monitoring the situation reported several airstrikes in the Aleppo region and near Raqqa, ISIS's de facto capital, just days after the truce took effect. 
 
 What are ramifications for disobeying ceasefire? 
 
 It's not immediately clear if there are any penalties in the current framework should any of the parties involved violate the ceasefire. 
 
 Under the terms of the cessation of hostilities in February , the agreement foresaw proportionate response in self-defense, if and when attacked. 
 
 What's at stake? 
 
 The lives of millions of Syrian people. ||||| In this photo released by the Syrian official news agency SANA, Syrians gather in a street that was hit by shelling, in the predominantly Christian and Armenian neighborhood of Suleimaniyeh, Aleppo, Syria,... (Associated Press) 
 
 MUNICH (AP) — Russia has proposed a March 1 ceasefire in Syria, U.S. officials say, but Washington believes Moscow is giving itself and the Syrian government three weeks to try to crush moderate rebel groups. 
 
 The United States has countered with demands for the fighting to stop immediately, the officials said Wednesday. Peace talks are supposed to resume by Feb. 25. 
 
 The talk of new ceasefire plans comes as the U.S., Russia and more than a dozen other countries meet in Munich to try to halt five years of civil war in the Arab country. The conflict has killed more than a quarter-million people, created Europe's biggest refugee crisis since World War II and allowed the Islamic State to carve out its own territory across parts of Syria and neighboring Iraq. 
 
 Russia says it is supporting Syrian President Bashar Assad's government as part of a counterterrorism campaign. But the West says the majority of its strikes are targeting moderate groups that are opposed to Assad and the Islamic State. 
 
 The most recent Russian-backed offensive, near Aleppo, prompted opposition groups to walk out of peace talks last month in Geneva, while forcing tens of thousands of civilians to flee toward the Turkish border. 
 
 The U.S. officials weren't authorized to speak publicly about private diplomatic discussions in the run-up to the Munich conference and demanded anonymity. One said the U.S. can't accept Russia's offer because opposition forces could suffer irreversible losses in northern and southern Syria before the ceasefire ever takes hold. 
 
 The officials said the U.S. counterproposal is simple: A ceasefire that is effective immediately and is accompanied by full humanitarian access to Syria's besieged civilian centers. 
 
 Secretary of State John Kerry, who arrived in Germany Wednesday, had talks planned late in the evening with U.N. peace envoy Staffan de Mistura and Adel al-Jubeir, the foreign minister of Saudi Arabia, a key backer of Syria's rebel groups. 
 
 The Obama administration has been trying for months to clinch a ceasefire and pave the way for a transition government in Syria that would allow parties to the conflict to concentrate on defeating the threat posed by the Islamic State and the al-Qaida-linked Nusra Front. 
 
 But after having long demanded Assad's ouster, the shift in the U.S. focus to combating terrorism has resulted in a confusing mix of priorities and a layered strategy in Syria that few understand, and even fewer see working. Beyond Russia, the administration has often struggled to keep its own allies such as Turkey and Saudi Arabia in line. 
 
 "We will approach this meeting in Munich with great hopes that this will be a telling moment," Kerry said Tuesday in Washington. His peace push coincides with Defense Secretary Ash Carter's attendance at a gathering in Brussels to hash out military options with NATO partners. 
 
 Brett McGurk, the Obama administration's point-man for defeating the Islamic State, said Russia's Aleppo offensive was having the perverse effect of helping the extremists by drawing local fighters away from the battle against IS and to the war against Syria's government. 
 
 "What Russia's doing is directly enabling ISIL," McGurk told the House Foreign Affairs Committee in Washington. 
 
 But the panel's top Democrat echoed some of the frustration of his Republican colleagues with the larger U.S. strategy. 
 
 "It seems as if we're only halfheartedly going after ISIS, and halfheartedly helping the (rebel) Free Syria Army and others on the ground," said Rep. Eliot Engel, D-N.Y. He urged a "robust campaign, not a tentative one, not one that seems like we're dragging ourselves in ... to destroy ISIS and get rid of Assad." 
 
 Kerry emphasized Tuesday that U.S. officials "are not blind to what is happening." He said the Aleppo battle makes it "much more difficult to be able to come to the table and to be able to have a serious conversation." 
 
 But the U.S. has staked its hopes for an end to the five-year civil war in Syria on the peace talks and Assad's eventual departure, saying the American public has no appetite for a military solution. 
 
 To that end, Washington has tempered its calls dating back to August 2011 for Assad to immediately leave power. And to get Russia on board, it now won't even say that Assad should be barred from running for re-election if and when a new Syrian constitution is drafted. 
 
 The ambiguity has emboldened Assad's supporters, Russia and Iran, while upsetting American allies in the Middle East, who are frustrated by a process that appears to lock the Syrian leader in place well into 2017 — and perhaps beyond.
– The latest attempt to bring peace to Syria has officially begun: A ceasefire brokered last week by the US and Russia went into effect Monday morning, reports the BBC. However, this being Syria—whose civil war is a many-sided conflict—it remained unclear just how effective it would be. The Syrian government and its main allies, Russia and Iran, say they will abide by the weeklong truce, but the country's most powerful insurgent groups have not yet said whether they will, reports AP. If the truce holds for a week, the US and Russia would begin intelligence sharing and target coordination against the Islamic State and al-Qaeda-linked militants. Meanwhile, Syrian President Bashar Assad vowed that his government would take back all its land from "terrorists." Assad spoke during a rare public appearance that included attending prayers for the Muslim holiday of Eid al-Adha in the Damascus suburb of Daraya, which had surrendered last month and reverted to government control after a four-year siege. "We call on all Syrians to turn toward reconciliation," he said. Italy, meanwhile, says a Syrian cease-fire could pave the way for political negotiations aimed at ending the long and bloody conflict. Foreign Minister Paolo Gentiloni told reporters after talks with his Cypriot counterpart that a cessation of hostilities must happen before talks can begin. CNN has a primer on the truce.