The UN Security Council has adopted a resolution demanding a 30-day cease-fire across Syria to allow aid deliveries and medical evacuations in conflict areas.
All 15 members of the council voted on February 24 in favor of a cessation of hostilities "without delay" following a flurry of last-minute negotiations on the text.
The move comes as, according to activists, Syrian government forces killed more than 500 civilians during a week of intense bombardment in eastern Ghouta, a rebel-held enclave near the capital, Damascus.
The British-based Syrian Observatory for Human Rights said warplanes struck Ghouta minutes after the Security Council adopted the resolution.
The two major rebel factions in Ghouta later welcomed the UN resolution, and pledged to protect aid convoys that come into the besieged enclave, Reuters news agency reported. There was no immediate reaction from Damascus.
Previous truce attempts have failed to take hold in the country, despite multiple rounds of international talks aimed at putting an end to the civil war.
Reports said the sponsors of the resolution, Kuwait and Sweden, amended the text to get Russian support, dropping a demand that the truce take effect in 72 hours.
Russia, a key ally of Syrian President Bashar al-Assad, has veto power on the security council.
The U.S. ambassador to the UN, Nikki Haley, called for the truce to be implemented immediately, but also expressed skepticism that the Damascus government would "allow humanitarian access to all of those who need it."
Russia's UN envoy Vassily Nebenzya said the cease-fire would not be possible without agreements between warring factions.
The vote had been postponed several times since February 22, with Western diplomats accusing Moscow of stalling for time.
Nebenzya has repeatedly argued that an immediate cease-fire was unrealistic. He also said the media and Western nations were conducting a "misinformation campaign" about the fighting in Ghouta and were ignoring what he called the "inconvenient truth" that several thousand Islamist fighters were still present in the region.
Russia, along with Iran, has given Assad's government crucial support throughout the 7-year-old war in Syria, which began with a government crackdown on protests.
Moscow helped turn the tide of the conflict in Assad's favor by launching a campaign of air strikes in 2015 and stepping up its military presence on the ground.
'Hell On Earth'
There has been a growing outcry from Western capitals, the United Nations, and humanitarian groups over the situation in Ghouta, which UN Secretary-General Antonio Guterres has called "hell on Earth."
The UN says nearly 400,000 people live in the region, a pocket of satellite towns and farms that has been under government siege for more than four years.
More than 2,400 people were said to have been injured there since government forces and their allies escalated their offensive on the Damascus suburb on February 18.
Ten hospital and medical centers have reportedly been knocked out of service due to the bombardment.
Meanwhile, Syrian state media said rebels in Ghouta have killed at least 16 civilians in eastern districts of the city over the past week.
At a news conference at the White House, U.S. President Donald Trump on February 23 accused Russia, Iran, and the Syrian government of being responsible for a "humanitarian disgrace" in Syria.
French President Emmanuel Macron and German Chancellor Angela Merkel appealed to Russian President Vladimir Putin to back the UN resolution and to press its Syrian government ally to stop the bombardments of Ghouta.
Turkish Foreign Minister Mevlut Cavusoglu said that "Russia and Iran must stop the regime."
He also said that the bombardment of eastern Gouta and a government offensive against rebel-held positions in Idlib Province was "contrary" to agreements negotiated in Astana by diplomats from Ankara, Moscow, and Tehran.