U.S. military officials have confirmed that a U.S. aircraft struck a mosque outside of Aleppo, Syria during evening prayers on Thursday, killing dozens of civilians, in an attack that many are calling a war crime.

Airwars’ Samuel Oakford reported that U.S. Central Command (CENTCOM) confirmed that a raid “took place in the vicinity of al-Jinah village, which is located in western Aleppo governorate, just a few kilometers from the border with Idlib. CENTCOM spokesperson Maj. Josh Jacques said the target was ‘assessed to be a meeting place for al Qaeda, and we took the strike.'”

Jacques added that the target “happened to be across the street from where there is a mosque.”

And Washington Post staff writer Thomas Gibbons-Neff reported:

US official: AQ strike in N. Syria involved two Reapers that fired roughly entirety of their Hellfire payload and followed up w/ 500lb bomb.

The U.K.-based Syrian Observatory for Human Rights said that at least 42 people were killed and dozens wounded. Local activists told Al Jazeera that “the mosque was full of worshippers,” with an estimated 300 people “inside at the time of the air raids.”

Rami Abdel Rahman, head of the Observatory, told the DPA news agency that most of those killed were civilians and that he fears “the number of casualties will increase” once rescuers are able to dig through the rubble.

Making no mention of civilian casualties, CENTCOM claimed the strike in Idlib “killed several al-Qaeda fighters,” according to Al Jazeera.

The death toll “appears to be at least the second largest ever from U.S. strikes aimed at alleged al-Qeada targets in Syria,” according to Oakford, as the intractable war against terror “enters its 16th year and third presidency, with no end in sight to the carnage,” as journalist Glenn Greenwald observed.

Reporting the reaction and how the strike might impact the fight against al-Qaeda in Syria, Charles Lister, a senior fellow with the Middle East Institute, wrote Thursday:

#pt: US strikes that hit mosques & kill 10s of civilians give AlQaeda even more of an advantage. Makes this worse:

#pt: #Qatar’s Foreign Minister calls the Al-Jinah Mosque airstrike “heinous” & says mosques “cannot be a place of murder or bloodshed.” pic.twitter.com/Xlzr0U3PVA

Turkish Deputy Prime Minister Numan Kurtulmus also condemned the attack as a war crime, telling reporters Friday: “This is a crime against humanity, this is a war crime. Bombing civilians, people in the mosque, and a house of worship is unacceptable.”

Article 53 of the Geneva Convention prohibits attacks on cultural objects and places of worship. Airwars confirmed that CENTCOM and the Pentagon are further investigating the attack.

The strike comes as U.S. President Donald Trump has taken steps to loosen constraints on military engagement, including lowering the standard for what defines an “acceptable” civilian casualty, as Common Dreams reported.