A U.S.-led military coalition

investigates whether an airstrike hit a Syrian prison after Syrian activists allege that a strike killed dozens of civilians there.

BEIRUT —Syrian activists say a coalition airstrike Monday on an Islamic State prison in eastern Syria killed dozens of prisoners.

The Syrian Observatory for Human Rights, a Britain-based group, said the airstrike killed 42 prisoners and 15 militants near Mayadeen in Deir el-Zour province.

The Deir Ezzor 24 media outlet, run by opposition activists, reported that 60 people had been killed. The prison housed those caught fighting the Islamic State, also known as ISIS.

Mayadeen is a city about 30 miles southeast of Deir el-Zour, an Islamic State stronghold frequently targeted in recent days by coalition aircraft as militant leaders fled there from Raqqa, the group’s de facto capital, and Mosul, Iraq.

Recent reports by local monitors in eastern Syria tell of other civilians killed by airstrikes.

A spokesman for the coalition acknowledged it had conducted strikes “on known ISIS command and control facilities and other ISIS infrastructure” in Mayadeen on Sunday and Monday. He said the group was investigating potential civilian casualties.

“The removal of these facilities disrupts ISIS’ ability to facilitate and provoke terrorist attacks against the coalition, our partner forces and in our homelands,” the spokesman said in a statement Tuesday. “This mission was meticulously planned and executed to reduce the risk of collateral damage and potential harm to noncombatants.”

The coalition’s civilian casualty assessment team will investigate the allegations, and its findings will be made public in monthly civilian casualty reports, the statement said.

The changes came after the coalition faced criticism for a strike March 17 that killed scores of civilians in west Mosul. Witnesses and rescuers insist that airstrike killed at least 278 civilians.