BEIRUT — The U.S. military said Tuesday it struck a mosque that had allegedly been used as an Islamic State control center, as American-allied Syrian forces battled the extremists in their last stronghold in eastern Syria amid reports of more civilian casualties.

The U.S.-led coalition said warplanes struck the mosque in the small town of Baghouz on Monday in support of the Kurdish-led Syrian Democratic Forces. It said the airstrike occurred as IS was using the mosque to direct attacks and employ suicide car bombs against the SDF.

“This mosque lost its protected status when ISIS deliberately chose to use it as a command and control center,” said the coalition’s deputy commander, Maj. Gen. Christopher Ghika.

Hundreds of mostly battle-hardened foreign IS fighters are believed to remain in Baghouz and nearby areas, where the SDF began its final push Saturday after months of fighting. IS has been fighting back with suicide car bombs, sniper fire and booby traps, and has been using civilians as human shields, slowing the U.S.-backed fighters’ advance.

Syrian state media reported that about 70 people were killed or wounded in an airstrike by the U.S.-led coalition on the edge of Baghouz. It said the airstrike hit a settlement where hundreds of people were taking shelter from the fighting.

The Britain-based Syrian Observatory for Human Rights, a war monitor, said seven children and eight women were killed late Monday in an airstrike near Baghouz. It was not immediately clear if they were referring to the same event.

At least 20,000 civilians have fled the last sliver of IS-controlled territory in just the past few weeks. The numbers have overwhelmed Kurdish-run camps in northeastern Syria, where humanitarian conditions are already dire amid a cold winter and meager resources.

IS militants, who once controlled a self-styled caliphate sprawling across large parts of Syria and neighboring Iraq, are now besieged from the north and east by SDF fighters, and are hemmed in by the Euphrates River to the west and south. Syrian government forces and their allies are deployed on the river’s west bank.

The capture of Baghouz and nearby areas would mark the end of a devastating four-year global campaign against the extremist group. U.S. President Donald Trump has said the group is all but defeated, and announced in December that he would withdraw all American forces from Syria.

However, activists and residents in eastern Syria say the militants are still present in recaptured areas, where they are laying the groundwork for a future insurgency .

Syrian activists who closely follow the conflict said negotiations are underway between IS and the SDF to open a corridor for the extremists to leave the besieged area.

The Observatory’s chief Rami Abdurrahman and Omar Abu Laila, who runs a group that monitors developments in the eastern province of Deir el-Zour, said the plan is to evacuate IS fighters into an area close to the Iraqi border.

The Observatory said the besieged IS commanders have about 40 tons of gold and cash worth millions of U.S. dollars that they hope to take with them.

The Sound and Picture organization, which reports on atrocities in IS-held areas, said an agreement for the evacuation was already reached. It said IS commanders agreed to reveal the fate of foreign hostages that were or are still held by the group and hand over some senior fighters.

The SDF spokesman was not immediately available for comment on possible negotiations.

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