A US-Russian-brokered ceasefire for south-west Syria held through the day in the first peacemaking effort of the war by the US government under President Donald Trump.
The United States, Russia and Jordan reached the "de-escalation agreement", which appeared to give Trump a diplomatic achievement at his first meeting with Russian President Vladimir Putin at the G20 summit in Germany this week.
The Syrian Observatory for Human Rights, a British-based war monitoring group, said "calm was prevailing," with no air strikes or clashes in the south-west since the truce began at noon on Sunday.
"The situation is relatively calm," said Suhaib al-Ruhail, a spokesman for the Alwiyat al-Furqan rebel faction in the Quneitra area.
Major Issam al Rayes, spokesman of the Southern Front coalition of Western-backed rebel groups, said "a cautious calm" continued into the evening.
Another rebel official, in Deraa city, said there had been no significant fighting. It was quiet on the main Manshiya front near the border with Jordan, which he said had been the site of some of the heaviest army bombing in recent weeks.
"Syrian ceasefire seems to be holding ... Good!" Trump tweeted on Sunday.
A Syrian official indicated that Damascus approved of the ceasefire deal, describing the government's silence over it as a "sign of satisfaction".
"We welcome any step that would cease the fire and pave the way for peaceful solutions," the government official said.
A witness in Deraa said he had not seen warplanes in the sky or heard any fighting since noon.
"We negotiated a ceasefire in parts of Syria which will save lives," Trump said in an earlier tweet on Sunday.
"Now it is time to move forward in working constructively with Russia!"
Russian Foreign Minister Sergei Lavrov said the truce included "securing humanitarian access and setting up contacts between the opposition in the region and a monitoring centre that is being established in Jordan's capital."
Ahead of UN-based peace talks set to open on Monday, a spokesman for the opposition delegation said in Geneva that the deal showed a "serious international effort to bring peace".