A US-led coalition air strike killed 20 civilians, including two children, overnight in a village near the Islamic State group's Syrian stronghold of Raqa, a monitor said Wednesday.
The Britain-based Syrian Observatory for Human Rights said dozens of people had also been wounded in the strikes on Tuesday night on the village of Al-Heisha, some 40 kilometres (25 miles) north of Raqa.
"The toll has risen to 20 civilians, including nine women and two children," Observatory chief Rami Abdul Rahman said.
The monitor had earlier given a toll of 16 dead.
Abdul Rahman said 32 people had also been injured in the strikes, adding that all the casualties were civilians.
Al-Heisha is controlled by IS group and has been a target of a new assault by the US-backed Syrian Democratic Forces (SDF) as it pushes to capture the militants' Syrian bastion of Raqa.
A spokeswoman for the Kurdish-Arab alliance dismissed the reports of civilian deaths.
"There is no such thing, and any such claims are IS news," Jihan Sheikh Ahmed told AFP.
The SDF's media account said at least six IS fighters had been killed by US-led coalition strikes in the village and accused the IS group of preventing civilians from leaving Al-Heisha in a bid to use them as "human shields."
The US-led coalition had no immediate comment on the report.
The SDF announced Sunday it had begun an operation to capture Raqa from IS group, as the militant group also comes under pressure across the border in Iraq, where its bastion Mosul is under attack.
Civilians fleeing Al-Heisha told AFP on Tuesday that IS fighters had brought heavy weaponry into the village when the SDF operation began.
"Daesh fighters brought heavy weapons to our village and stayed among us so that if there were strikes they would hit us," 45-year-old Saada al-Aboud said.
"They wouldn't let us leave. We had to escape by running out into the fields, with our children and old people. What else could we do? We left everything behind."