The US military has denied reports that it bombed a mosque in north-western Syria during evening prayers.
The UK-based Syrian Observatory for Human Rights monitoring group said 46 people, mostly civilians, died in an air strike on what it said was a mosque.
The US military said it had carried out an air strike, killing several al-Qaeda militants, but did not hit a mosque.
It said it was looking into reports of civilian casualties.
“We did not target, nor did we strike a mosque,” Major Josh Jacques, a spokesman for US Central Command (Centcom) told the BBC.
“We targeted an al-Qaeda gathering across the street from a mosque. The mosque does not appear to be damaged following the strike. We are aware of the reports of civilian casualties and we are looking into it,” he said.
In an earlier statement to AFP news agency, he said the meeting site the US targeted was about 50ft (15m) from the mosque.
A correspondent for the agency described watching rescue workers dig people out of the rubble late on Thursday.
A building with a dome and loudspeaker can be seen largely intact close to the rubble in pictures of the scene. In another picture, a black placard naming a mosque and Islamic law school leans against a damaged building.
The UK-based observatory, which relays information from sources on the ground, said the al-Jineh mosque had been packed with worshippers for evening prayers.
The US military originally said the strike had taken place in neighbouring Idlib province, but later said it was in Aleppo province.
The village lies in one of the main rebel-held regions of Syria. Russian and Syrian aircraft operate in the area and US warplanes also target jihadist rebels in the region.
The attack on Thursday came only a day after at least 31 people were killed in a suicide bombing at the main court complex in the capital, Damascus.
The Damascus bombing was on the sixth anniversary of the start of the uprising against President Bashar al-Assad.
Since then, more than 320,000 people have been killed and 11 million displaced in the conflict, according to activists.
Syria air strike: Mosque was not bombed, insists US}