A 10-day truce is meant to start on Monday, followed by co-ordinated air strikes against jihadist militants.
Turkey and the EU welcomed the plan but warned that further action was needed.
Turkey said aid must be delivered from the very start while EU foreign policy chief Federica Mogherini looked towards a "political transition".
A spokeswoman for Syria`s opposition said the plan provided some hope but more details were needed about how it would be enforced.
In the capital, Damascus, the government endorsed the deal, the state news agency Sana reported.
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