The Syrian armed opposition command has said it will impose a curfew in Damascus, starting at 4 p.m. local time (1300 UTC/GMT) till 5 a.m. on Monday.
The Military Operations Administration, which posted the decision on Telegram, did not state a reason for the curfew.
Russia: Assad has resigned and left Syria
The Russian Foreign Ministry on Sunday said Syrian leader Bashar Assad has left his post and the country.
Without commenting on Assad's actual location, the ministry's statement said he left Syria after giving orders there be a peaceful handover of power.
"As a result of talks between B. Assad and a range of participants of the conflict on the territory of the Syrian Arab Republic, he took the decision to resign from his presidential post and leave the country, giving instructions to proceed with the peaceful transfer of power," Russia's Foreign Ministry said.
The ministry added that Russia has not taken part in the talks concerning his departure.
Russia was a staunch Assad ally and intervened in 2015 to prop him up during the civil war. But with its military focus shifted to the war in Ukraine, Russia's ability to influence the situation on the ground was far more limited.
Konstantin Kosachyov, deputy chairman of Russia's upper house of parliament, suggested that Moscow was willing to support the Syrian people but would likely not engage militarily as it had in the past.
"If the people of Syria continue to need our support, it will be provided," he said. "But hardly in the context of a full-scale civil war. The Syrians will have to deal with that themselves."
UK's Starmer welcomes fall of 'barbaric regime'
British Prime Minister Keir Starmer called for all sides to protect Syrian civilians and ensure aid can reach those in need after Assad's sudden fall.
"The developments in Syria in recent hours and days are unprecedented, and we are speaking to our partners in the region and monitoring the situation closely," Starmer said.
"The Syrian people have suffered under Assad's barbaric regime for too long and we welcome his departure. Our focus is now on ensuring a political solution prevails and stability is restored," he said.
Starmer also joined several other world leaders in urging all sides to "protect civilians and minorities," as well as ensuring that "essential aid can reach the most vulnerable in the coming hours and days."