Four more people have died of injuries sustained in airstrikes on a marketplace in Idlib in north-western Syria, bringing the death toll to 62 civilians, a monitoring group says.
Unidentified jets bombarded the market in the rebel-held city on Saturday hours after the United States and Russia announced a ceasefire agreement for Syria, the Syrian Observatory for Human Rights added.
The watchdog on late Saturday had put the death toll at 58 civilians.
The dead included 13 children and 13 women, according to the Observatory, which relies on a network of activists inside Syria.
The attack, which the opposition called a "massacre", is believed to have been carried out by government jets or those of allied Russia.
Idlib is mostly controlled by rebels including the Jabhat Fatah al-Sham, a former al-Qaeda affiliate previously known as al- Nusra Front.
The US and Russia on Friday sealed a plan for Syria that includes a nationwide truce set to start at sunset on Monday.
The agreement also envisages unprecedented US-Russian military co-ordination against militant groups in Syria, including Islamic State and Jabhat Fatah al-Sham.
Al-Assad's government has endorsed the plan, while the opposition has voiced doubts on whether the new ceasefire will hold.
A truce brokered by the US and Russia in February did not hold for long in Syria.
Iran, an ally of al-Assad, welcomed the latest ceasefire agreement on Sunday.
Syria's conflict started with peaceful anti-government protests in March 2011. It soon spiralled into a full-blown war that has claimed more than 250,000 lives, according to activists' estimates.
