In one of the bloodiest attacks on Iraq's fledgling security forces, the unarmed recruits were shot in the back of their heads after being stopped by guerrillas posing as policemen as they traveled home for leave in the northeast of the country.

"There was an ugly crime in which a large group of National Guards were martyred," Prime Minister Iyad Allawi told Iraq's national assembly.

"We believe this issue was the outcome of major neglect by some parts of the multinational (forces)," he said without elaborating.

A statement by the U.S.-led multinational forces in Iraq blamed the killings on "terrorists."