KABUL, Afghanistan — Government officials in southern Afghanistan said on Monday that as many as 40 civilians, including children, may have been killed during an American-supported Afghan military raid on an insurgent stronghold the night before.

Accounts from the scene, in Helmand Province, were fragmentary and contradictory, typical of violent clashes in which civilians are reported killed in remote areas late at night. Scores of civilians have died in recent weeks in Taliban suicide attacks in civilian areas and in American and Afghan airstrikes targeting insurgents.

A defense official in Washington conceded that civilians had probably been killed Sunday night, possibly by secondary explosions from an insurgent weapons depot attacked by American warplanes.

The fighting on Sunday took place in an area controlled by the Taliban, making it difficult to reach witnesses.