The United States and Russia reached a deal on a new Syrian ceasefire, which, if it holds, could see the first joint military effort by the two powers against jihadists.
U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov said that the truce, reached late on Friday, would come into force on Monday, the first day of the Muslim holiday of Eid al-Adha.
The two powers back opposite sides of the conflict, with Moscow supporting the regime of President Bashar Assad and the U.S. behind a coalition of rebel groups it regards as moderate.
But 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 "terrorist" 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.
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 to the five-year civil war that has killed 290,000 and displaced half the country's population.