UK-based monitoring group says nine women and two children were among the dead, and 32 others have been injured.
An US-led coalition air strike has killed 20 civilians in a northern village of Daesh's de facto capital Raqqah in Syria, a Britain-based war monitoring group said.
The Syrian Democratic Forces (SDF), a militia supported by Washington, has been advancing on the city of Raqqah, Daesh's self-proclaimed capital in Syria. The offensive to free the city comes at a time when a similar push is underway against Daesh in Mosul, Iraq.
Rami Abdul Rahman, the head of the Syrian Observatory for Human Rights, said on Wednesday that a coalition strike overnight had hit the Daesh-held village of Al-Heisha, about 40 kilometres (25 miles) north of Raqqah.
Nine women and two children were among the 20 civilians killed and 32 others were wounded, Rahman said.
However, the SDF denied any civilian deaths.
"There is no such thing, and any such claims are IS [Daesh] news," SDF spokeswoman Jihan Sheikh Ahmed said.
US Colonel John Dorrian, a spokesman for the coalition, told AFP it appeared there had been strikes in the area.
"After an initial assessment... the coalition confirms it did conduct strikes in the area described in the allegation," he said.
"However, more specific information is needed to conclusively determine responsibility" for civilian casualties.
The Observatory said the latest deaths brought the number of civilians killed since coalition-led air strikes in Syria began in September 2014 to 680, including 169 children.
Meanwhile, the Pentagon said late Wednesday that air strikes in both Syria and Iraq may have killed 119 civilians since 2014, a figure far lower than estimates by a number of monitoring groups.