U.S. military officials watched live drone feeds in October that appeared to show Turkish-backed Arab gunmen targeting civilians during their assault on Kurdish fighters in northeastern Syria, attacks the Americans reported to their commanders as possible war crimes, current and former U.S. officials familiar with the incidents said.

U.S. surveillance videos of two incidents were included in an internal report compiled by State Department officials laying out concerns regarding four credible cases of alleged war crimes by Turkish-backed forces, the U.S. officials said.

The existence of the military surveillance videos, which hasn’t been previously disclosed, provided what some of the U.S. officials saw as firsthand evidence of apparent war crimes by forces backed by Turkey, an ally in the North Atlantic Treaty Organization. Others said the videos were inconclusive.

The footage now has become a focal point of a broader debate within the Trump administration over how to address mounting concerns by U.S. officials that the Turkish-backed fighters could commit more war crimes if the U.S. doesn’t do more to stop them.

The possible war crimes and other issues related to Turkey’s incursion are expected to arise during a White House visit on Wednesday by Turkish President Recep Tayyip Erdogan. Mr. Erdogan has vowed to investigate reports of war crimes, but some U.S. officials say they doubt Turkey will take the issue seriously.