Nouri al-Maliki, the Iraqi prime minister, said on Thursday that the deaths of 24 Iraqis in the western town of Haditha last November, apparently at the hands of US marines, was a "terrible crime".
His coalition government said a national security committee would work with US forces to make sure there was no repeat of the incident.
"The crime and misery of Haditha ... is a terrible crime where women and children were eliminated," the prime minister said.
Al-Maliki had said on Tuesday that his patience was wearing thin with excuses that US troops kill civilians "by mistake", and that he wanted an investigation into Haditha and other similar cases.
The US president, meanwhile, said that he would punish those responsible if an internal military investigation verifies allegations that marines rampaged through houses in Haditha on November 19 and shot civilians, including women and children.
"I'm not involved with the investigation," Bush told reporters after a cabinet meeting. "And you shouldn't expect me to be. I expect this investigation to be conducted independent of the White House, with a full and thorough investigation.
"Obviously, the allegations are very troubling for me and equally troubling for our military, especially the Marine Corps."
Preliminary forensic evidence from the military showed that the Haditha victims had bullet wounds, contradicting earlier statements from marines that they had been killed by roadside bombs, according to US officials who spoke on condition of anonymity.
Maliki's patience is wearing thin
Some have accused the military of a cover-up and called for an independent investigation.
Several commentators in the US media have drawn parallels between the Haditha incident and the 1968 killings of nearly 500 unarmed civilians by US troops in the village of My Lai during the Vietnam War.
US military commanders have now ordered ethics training for combat troops over the next 30 days in "core warrior values".
Bush said the training has been ordered to reinforce procedures and standards.
"Our troops have been trained on core values throughout their training," Bush said.
"This is just a reminder for troops either in Iraq or throughout our military that there are high standards expected of them, and that there are strong rules of engagement."