Parties would indicate their agreement to the United States and Russia by noon on Friday Damascus time (1000 GMT), and the truce would go into effect at midnight, the two countries said in a joint statement issued by the U.S. State Department.
Under the terms of the deal, Syrian government and allied forces will cease attacks against armed opposition forces, and vice versa, with any weapons including rockets, mortars, anti-tank guided missiles.
However, the U.S.-Russian plan leaves a loophole by allowing continued attacks, including air strikes, against Islamic State, Nusra and other militants. Because of the mingling of forces, this could result in continued attacks against armed opposition members who are parties to the cessation of hostilities.
"Military actions, including air strikes, of the Armed Forces of the Syrian Arab Republic, the Russian Armed Forces, and the U.S.-led Counter ISIL Coalition will continue against ISIL, 'Jabhat al-Nusra' (Nusra Front) and other terrorist organizations designated by the UN Security Council," the joint statement said.
It added that Russia, the United States and others would work together to delineate the territory held by Islamic State, Nusra Front and other groups deemed terrorists by the U.N. Security Council which are excluded from the truce.