U.S. drone aircraft fired missiles and dropped a 500-pound bomb outside Aleppo on Thursday in an attack that the Pentagon said killed scores of al-Qaeda 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 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-Qaeda 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-Qaeda presence there.

U.S. aircraft have struck dozens of locations in northwest Syria, where an al-Qaeda-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-Qaeda fighters. He said there was a mosque nearby but it had not been hit.

A U.S. official, speaking on the 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-Qaeda 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. 

The mosque was believed to have housed several displaced families from the nearby city of Aleppo, much of which was leveled by Syrian government forces during an extended campaign to recapture the eastern half of the city from opposition forces. 

“Whether U.S. drones directly targeted the mosque at al-Jinah, as some allege — or it was instead caught up in a U.S. drone strike in the immediate vicinity — a significant number of civilians died at the scene, according to the White Helmets, local media and casualty monitors,” said Chris Woods, director of Airwars, a Britain-based group that tracks allegations of civilian casualties.

The organization said the rate of civilian deaths caused by U.S.-led coalition airstrikes, as well as unilateral U.S. actions, had been rising “steeply” in Syria and Iraq.

“Minimizing harm to noncombatants on the battlefield needs to remain a central priority, not an afterthought,” Woods said.

While the U.S. military has placed an emphasis on avoiding civilian deaths since the Islamic State operation began, it has acknowledged at least 200 such casualties since 2014.

Now, U.S. officials are reviewing whether to roll back rules, put in place by President Barack Obama, that subject counterterrorism strikes to close scrutiny by the White House and require the United States to have “near certainty” that strikes outside war zones will not kill civilians.

The change would hand greater decision-making power back to the Defense Department and CIA, but activists say it would also alienate people in countries with counterterrorism problems and create additional national security threats in the long run.

It is not clear whether the strike in Jinah would have been affected by any changes to those rules.

Six years after the Syrian conflict began, neither the government, backed by Russia and Iran; a small moderate rebel force backed by the United States; nor an array of other armed groups appears to have a clear path to victory.

The northwestern provinces of Idlib and Aleppo are home to hundreds of thousands of civilians displaced by fighting between forces loyal to Syrian President Bashar al-Assad and rebels present in a shrinking sliver of territory along the country’s border with Turkey. 

In addition to U.S. aircraft, Russian and Syrian aircraft are also known to operate in the area, turning the battlefield into a microcosm of the geopolitical tensions that have come to define Syria’s long war. 

As the conflict has dragged on, it has allowed Tahrir al-Sham, with its deep ties to al-Qaeda, to play an increasingly powerful role.

The expanding U.S. campaign against al-Qaeda in Syria is believed to have spread fear among the group’s ranks. Its second-in-command in Syria, Abu al-Khayr al-Masri, was killed in an airstrike on his car in late February. The U.S. Central Command said a separate bombing raid on an al-Qaeda training camp in January killed more than 100 militants.

Activists and journalists in northeastern Syria said the group has become more cautious about large gatherings, including those such as the one the U.S. military described as taking place Thursday in Jinah. Members often choose to travel by motorcycle instead of by car, and without circulating movement plans ahead of time.

Gibbons-Neff and Ryan reported from Washington. Heba Habib in Stockholm and Zakaria Zakaria in Sanliurfa, Turkey, contributed to this report.