United States and Russia agreed a deal to impose a ceasefire in Syria, and if the truce holds they will begin a joint military effort against terrorists. 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 U.S. Behind a coalition of rebel groups. But if Russia is able to use its leverage over Assad to respect the ceasefire for a week, Moscow and Washington will begin joint air strikes against agreed terrorist targets. The much anticipated breakthrough came at the end of marathon talks between Lavrov and Kerry in Geneva. John Kerry said United States and Russia Are announcing a plan which will reduce violence, ease suffering and resume movement towards a negotiated peace and a political transition in Syria. Russian Foreign Minister Sergei Lavrov said United States and Russia have agreed to carry out joint air strikes in Syria if a newly agreed ceasefire holds for a week.