Air strikes on the Islamic State group's de facto Syrian capital Raqa killed 25 civilians, six of them children, a monitoring group said on Wednesday.
"Dozens more were wounded, some of them critically," the Syrian Observatory for Human Rights said, adding it was not immediately able to determine who carried out the Tuesday raids.
The Syrian government, its ally Russia and a US-led coalition have all carried out air strikes against IS in Raqa.
The Observatory said there were fresh air strikes against the city on Wednesday, one of which hit the town hall. It said those strikes appeared to have been carried out by the coalition.
The coalition said it had carried out two strikes near Raqa on Monday, hitting a bridge used by the jihadists as well as oil facilities.
There are an estimated 300,000 people still living in the city.
Activists have accused IS of preventing civilians from leaving in order to use them as human shields against air strikes.
Twin offensives aimed at severing IS's supply route to Raqa from the Turkish border have met fierce resistance from the jihadists in recent days.
Near the border, a US-backed alliance of Kurdish and Arab fighters has been encircling IS in the town of Manbij for days but has faced multiple suicide bombings by the jihadists.
At least three IS suicide bombers attacked the Syrian Democratic Forces near Manbij on Tuesday, the Observatory said.
A separate Russian-backed offensive by government forces targeting the town of Tabqa, 40 kilometres (25 miles) up the Euphrates Valley from Raqa, suffered a major reverse on Monday.
More than 40 troops and militia were killed in a jihadist counterattack launched on Sunday.
The government forces, which had advanced to within seven kilometres (four miles) of Tabqa airbase, were driven back an estimated 20 kilometres (12 miles) to the west.
IS has also been under attack in neighbouring Iraq. It has been driven out of the centre of its emblematic bastion Fallujah and pro-government forces have also renewed an offensive around Mosul, the largest city under its control.