The United Nations Security Council adopted a resolution on Saturday demanding a 30-day truce in Syria to allow aid deliveries and medical evacuations with the support of Syrian ally Russia after a flurry of last-minute negotiations.
The vote comes as warplanes pounded eastern Ghouta, the last rebel enclave near Syria's capital, for a seventh straight day.
U.N. Secretary-General Antonio Guterres appealed on Wednesday for an immediate end to "war activities" there.
According to the Syrian Observatory for Human Rights the air strikes have killed more than 500 people over the last week.
The dead included more than 120 children.
The Britain-based monitor said raids hit Douma, Zamalka and other towns there on Saturday killing 31 people.
The surge of air strikes and shelling by the Syrian government is one of the fiercest air-assaults of the country's seven-year war.