President Bush says he is troubled by allegations U.S. Marines killed unarmed Iraqi civilians last year in the city of Haditha.  Mr. Bush says if laws were broken, those responsible will be punished.

The president says the initial reports of abuse are troubling.  He promises a full investigation.

"If in fact laws were broken, there will be punishment," said Mr. Bush.

Marine General Peter Pace salutes as President Bush arrives on stage for a Memorial Day ceremony at Arlington National Cemetery

Speaking to reporters after a meeting with the President of Rwanda, Mr. Bush made clear he wants answers, and so does the Marine Corps.  He said he has discussed the matter at length with the nation's top military officer, Joint Chiefs of Staff Chairman Peter Pace.

"He is a proud Marine and nobody is more concerned about these allegations than the Marine Corps," he added.

It was the president's first public comment on reports Marines killed as many as two dozen unarmed Iraqis last November in Haditha, a city in Western Iraq that has been plagued by insurgents.

The reports say the Marines opened fire after a bomb rocked a military convoy, killing one member of their squad.  The Marine Corps had initially attributed 15 civilian deaths to the bombing and a gun battle with insurgents.

The Bush administration says the military investigation will be thorough, and has promised to share the results with the public.