At least 13 people, including six children, have been killed in a United States special operations forces raid in Syria’s rebel-held Idlib province, according to residents and first responders.

The overnight raid targeted a building in Atmeh, a densely populated town in northwest Syria near the Turkish border, where tens of thousands of people displaced by the country’s decade-long war live. There was no immediate information about the identity of those living in the building. Unconfirmed reports said the target was an al-Qaeda-affiliated fighter.

“We woke up at 1am to the sound of helicopters … and then at around 3am we heard a barrage of attacks,” Abu Fahed al-Homsi, a displaced Syrian who lives a block away from the target, told Al Jazeera on Thursday.

“We saw a house that was targeted and damaged roads, but we still have no idea what was going on.”

Residents said the helicopters were hovering over the building for more than two hours, before hitting it with missiles. The US special forces then carried out a landing operation and stormed the house.

Mahmoud Chehadi, who lives nearby, said the US forces had surrounded the targeted building and used loudspeakers to call on its residents to leave the area.

“When the operation ended, we went to the area and saw a woman who apparently detonated an explosive vest, and inside the building, we saw some bodies, including [that of] a man and a child,” he told Al Jazeera.

The Syrian Civil Defense, a volunteer rescue group operating in rebel-held parts of Syria that is also known as White Helmets, said in a statement at least 13 people were killed, including four women.

Local activists and residents quoted by news agencies said fighters in the area clashed with US forces.

The Pentagon did not give any details about the raid but, in a statement, it said the “mission was successful”.

“U.S. Special Operations forces under the control of U.S. Central Command conducted a counter-terrorism mission this evening in northwest Syria,” Pentagon Press Secretary John Kirby said.

“There were no U.S. casualties. More information will be provided as it becomes available.”

Idlib province in northwestern Syria is the last rebel-held stronghold in the war-torn country, mostly controlled by former al-Qaeda-affiliate Hay’et Tahrir al-Sham.

US-led coalition operations against remnants of ISIL (ISIS) sleeper cells are more frequent in northeastern Syria, under the control of the Kurdish-led Syrian Democratic Forces.

For years, the US military has also used drones to kill top al-Qaeda operatives in northern Syria, where the fighter group became active over the course of the war that began as a mass uprising against President Bashar al-Assad but quickly morphed into a full-fledged conflict.

The latest strike comes a week after US Secretary of Defense Lloyd Austin issued a directive ordering military leaders to do more to protect civilians from harm in drone attacks and other combat operations.

The US military has come under renewed pressure to reform its policies following a August strike that killed 10 members of a family in Afghanistan, including several children.

Meanwhile, a December investigation by the New York Times concluded, based on a trove of confidential Pentagon documents, that US air wars in the Middle East have been marked by “deeply flawed intelligence” and “faulty targeting” that has resulted in the deaths of more than 1,000 civilians over the last decade.