BEIRUT — U.S. drone aircraft fired missiles and dropped a 500-pound bomb outside Aleppo on Friday in an attack that the Pentagon said killed scores of al-Qaida militants but that local residents described as an assault on a mosque crowded with civilians.

U.S. officials said the strikes in the town of Jinah had killed “dozens” of militants at a meeting of the terrorist group. But local activists and a monitoring group reported that at least 46 people died, and more were trapped under rubble, when the attack struck a mosque during a religious gathering.

The Syrian Observatory for Human Rights, a Britain-based monitoring network, described the scene in Jinah as a “massacre,” saying the dead were mostly civilians. Photos from the area showed rescue workers pulling mangled bodies from a mound of rubble.

“Bodies filled the space,” said Mohamed al-Shaghal, a journalist who arrived at the scene shortly after the attack. He said the mosque had been destroyed.

The disputed strike occurred as the Trump administration makes plans to expand its troop presence in Syria, part of a push to intensify counterterrorism operations across the Middle East, and weeks after a U.S. operation against al-Qaida left civilians dead in Yemen.

It also takes place as the White House considers lifting rules enacted by the Obama administration that sought to avoid civilian deaths, another sign of President Trump’s more aggressive approach to dealing with terrorist threats overseas.

If confirmed, Thursday’s killing of civilians would mark one of the worst instances of errant deaths alleged against the United States since it began its air campaign in Iraq and Syria more than two years ago. Pentagon officials said they had no credible allegations of civilian casualties in the strike but would begin an investigation if any surfaced.

While the ongoing U.S. air campaign in Syria has mostly targeted the Islamic State, the U.S. military has also launched a parallel effort against what is described as a growing al-Qaida presence there.

U.S. aircraft have struck dozens of locations in northwest Syria, where an al-Qaida-linked alliance of rebel groups known as Tahrir al-Sham, or HTS, is now the ascendant force. The area is also home to an assortment of other rebel groups active in Syria’s ongoing civil war.

Residents in Jinah described powerful blasts Thursday night that shook the ground and sent civilians fleeing, many of them dazed and bleeding. Three residents said that at the time of the attack at least 200 people were gathered in the mosque and a nearby building for religious instruction.

Aerial imagery appeared to confirm that much of the northern section of Jinah’s mosque was destroyed, although it was unclear whether the strike was a direct one.

Navy Capt. Jeff Davis, a Pentagon spokesman, told reporters that the American munitions struck a “partially constructed community hall” that was being used by al-Qaida fighters. He said there was a mosque nearby but it had not been hit.

A U.S. official, speaking on condition of anonymity because he was not authorized to comment on the record, insisted the decision to conduct the strike was based on verified intelligence. He said that militants had gathered to discuss future operations.

Eric Pahon, another Pentagon spokesman, said the fighters used the half-built hall “as a place to educate and indoctrinate al-Qaida fighters.”

Thursday’s attack involved two Reaper drones, which fired more than four Hellfire missiles and dropped at least one 500-pound guided bomb in a follow-up strike, the U.S. official said.

Mohamed Shakourdi, a local activist, said the final explosion came as people streamed out of the mosque. “They were running as a fourth rocket hit,” he said.