Marines from 3rd Battalion, 3rd Marine Regiment conducting a foot patrol through streets of Haditha (file photo)

The U.S. military in Iraq has ordered American commanders to conduct core values training on legal, moral and ethical standards on the battlefield.

The order came as the military investigates whether U.S. Marines intentionally killed as many as 24 unarmed Iraqi civilians last year in the town of Haditha.

In a written statement, Lieutenant General Peter Chiarelli - the number-two U.S. commander in Iraq - said the training would emphasize "professional military values and the importance of disciplined, professional conduct in combat."

In Washington Thursday, President Bush said U.S. troops receive training on values throughout their careers. He told reporters the current training is what he called a reminder.  Mr. Bush repeated that he is concerned by the Haditha allegations, and that there will be a full and complete investigation.

The New York Times reports the military investigation of the incident in Haditha contradicts claims by Marines that 15 civilians were killed by a roadside bomb and an ensuing gun battle with insurgents.

News reports say Marines killed civilians after a member of their squad was killed in a roadside bomb blast in Haditha.

Iraqi Prime Minister Nouri al-Maliki has denounced the alleged killings and said he would launch his own investigation.