US and Russia clinch ceasefire deal

"Today, Sergei Lavrov and I, on behalf of our president and our countries call on every Syrian stakeholder to support the plan that the United States and Russia have reached, to ... bring this catastrophic conflict to the quickest possible end through a political process," US Secretary of State John Kerry said.

Russian Foreign Minister Sergei Lavrov said that despite continuing mistrust, the two sides had developed five documents that would enable coordination of the fight against armed groups and a revival of Syria's failed truce in an enhanced form.

"This all creates the necessary conditions for resumption of the political process which has been stalling for a long time," Lavrov told a news conference.

The two powers back opposite sides of the conflict, with Moscow supporting the government of President Bashar al-Assad and the US behind a coalition of rebel groups.

If Russia is able to pressure Assad to respect the ceasefire for a week, Moscow and Washington will set up a joint coordination unit and begin air strikes against agreed targets.

"We will jointly agree on strikes against terrorists to be carried out by the Russian and American air forces. We have agreed on the zones in which these strikes will be carried out," said Lavrov.

Marathon talks

The much anticipated - if tentative - breakthrough came at the end of marathon talks between Lavrov and Kerry in Geneva, as the pair push for an end of the five-year civil war.

"Today, the United States and Russia are announcing a plan which we hope will reduce violence, ease suffering and resume movement towards a negotiated peace and a political transition in Syria," Kerry said.

The vexed question of Assad's fate remains, with Western powers calling for his removal and Russia backing him.

Key to the deal is the withdrawal of Syrian government forces around rebel-held Aleppo, allowing desperately needed humanitarian access to besieged communities.

The High Negotiations Committee, an umbrella group of the Syrian opposition, on Saturday welcomed the deal, saying it hoped it would bring relief to hundreds of thousands civilians.

"We hope this will be the beginning of the end of the civilians' ordeal," HNC spokeswoman Bassma Kodmani said. "We welcome the deal if it is going to be enforced."

Russia also needs to persuade the Syrian air force to stop strikes on anti-government positions, which have also killed large numbers of civilians.

In turn, Washington has to get the opposition groups it backs to separate themselves from Jabhat Fateh al-Sham, which has allied itself with a range of rebels at different points in the fluid conflict.

Only if commitments by Moscow and the Assad government to cease violence for seven days are "fully met" will the US and Russia start cooperating with joint strikes, the Pentagon said in a statement following the announcement.

Lavrov cautioned that Moscow could not "100 percent guarantee" that all the parties would obey the ceasefire.

"The Syrian Government has been informed by us about these arrangements, and it is ready to fulfil them," he added.

END