The US said it carried out an air strike in Syria against an Al-Qaeda meeting but denied deliberately targeting a mosque where a monitor said on Friday 46 people were killed.
The Syrian Observatory for Human Rights said most of the dead in the Thursday evening raid on Al-Jineh, in the northern province of Aleppo, were civilians.
The US-led coalition has been bombing jihadist groups in war-torn Syria since 2014, with hundreds of civilians unintentionally killed in the country and in neighbouring Iraq.
"We did not target a mosque, but the building that we did target -- which was where the meeting took place -- is about 50 feet (15 metres) from a mosque that is still standing," said Colonel John J. Thomas, spokesman for US Central Command.
According to a Centcom statement: "US forces conducted an air strike on an Al-Qaeda in Syria meeting location March 16 in Idlib, Syria, killing several terrorists."
The Centcom spokesman later clarified that the precise location of the strike was unclear -- but that it was the same one widely reported to have hit the village mosque in Al-Jineh, in Aleppo province.
"We are going to look into any allegations of civilian casualties in relation to this strike," he added.
An AFP correspondent saw rescue workers in white helmets working under spotlights with picks and shovels late on Thursday to dig people out of the rubble.
Much of the mosque, identified by a black placard outside as a mosque, had been flattened.
The empty prayer hall was covered in debris, and rescue workers stepped through it carefully, deliberating how to break down a wall to search for more survivors.
Rescuers had earlier left the wreckage site but were forced to double back when they heard moaning coming from the rubble.
Some bodies 'unrecognisable'
"More than 100 people were wounded," Observatory head Rami Abdel Rahman said on Thursday, adding that many were still trapped under the collapsed mosque in the village of Al-Jineh, just over 30 kilometres (20 miles) west of Aleppo.
The village is held by Islamist groups, but the Observatory said no jihadist factions are present.
Abu Muhammed, a village resident, told AFP that he "heard powerful explosions when the mosque was hit. It was right after prayers at a time when there are usually religious lessons for men in it.
"I saw 15 bodies and lots of body parts in the debris when I arrived. We couldn't even recognise some of the bodies," he added.
More than 320,000 people have been killed in Syria since the conflict with anti-government protests six years ago.
A ceasefire between government forces and non-jihadist rebel groups was brokered by rebel backer Turkey and regime ally Russia in December, but violence has continued.
The Observatory, which relies on a network of sources inside Syria for its information, says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.
But the skies over Aleppo province are busy, with Syrian regime and Russian warplanes as well as US-led coalition aircraft carrying out strikes.
Russia began a military intervention in Syria in September 2015, and in the past has dismissed allegations of civilian deaths in its strikes.
The US-led coalition fighting the Islamic State group said earlier this month that its raids in Iraq and Syria had unintentionally killed at least 220 civilians since 2014.
Critics say the real number is much higher.