KABUL, Afghanistan - A senior Afghan militia commander alleged Wednesday that troops from Afghanistan's U.S.-trained national army beheaded four Taliban fighters to avenge the similar slaying of an Afghan soldier and a military interpreter.

The killings occurred Monday in the Arghandab district of southeastern Zabul province, said Naimatullah Khan, the commander of government militias in the province. U.S. troops were not present at the time, Khan said.

Afghan National Army troops sent to look for an interpreter and soldier who became separated from a combined Afghan-U.S. force found their corpses and severed heads on a mountainside, Khan said. Four Taliban fighters were later caught in a search of the area, he said.

"The ANA soldiers did the same thing. They cut off their heads," Khan said. He said the corpses of the suspected Taliban were left where they lay, but had no further details.

If verified, the decapitations would mark an escalation in violence plaguing much of the south and east, especially Zabul, in recent weeks. The U.S. military says it has killed more than 80 rebels since May 25.

It would also be a setback for the American-led attempt to build a disciplined, professional Afghan fighting force so that foreign troops can ultimately leave. The national army currently numbers about 10,000, far short of the projected 70,000.

American soldiers typically accompany Afghan army units during operations, but Lt. Col. Tucker Mansager, a spokesman for the U.S. military, said today it had "no independent confirmation" that the beheadings occurred. He declined to comment further.

Afghan military and government officials in Kabul were not available for comment.