US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov said the truce 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 al-Assad and the US 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.