The U.S. Defense Department has refused to confirm or deny a charge by a senior member of Congress, who says an investigation has concluded that a group of U.S. troops in Iraq killed at least 15 civilians during an incident last year. The department says the investigation of the incident is still in progress.

The incident took place last November in the Iraqi town of Haditha. It was first reported several months later, and a preliminary military investigation in February recommended that a formal criminal investigation be launched. Officials say that probe is still underway.

According to the military, 15 Iraqi civilians died in the incident as a result of an explosion caused by an insurgent bomb, what the military calls an IED, or Improvised Explosive Device, that had also killed one of the Marines. Other reports charged that the U.S. Marines on the scene shot the civilians to retaliate for losing their comrade.

Rep. John Murtha

On Wednesday, Representative John Murtha, said the military investigation indicates the Marines did kill the civilians and for no reason.

"There was no firefight," he said. "There was no IED that killed these innocent people. Our troops over-reacted because of the pressure on them. And they killed innocent civilians in cold blood."

Congressman Murtha also said the civilian death toll was 24, not 15 as the Marines first reported. Murtha is a former Marine, a respected expert on defense issues and a strong supporter of the military. Six months ago he called for the Bush administration to withdraw U.S. troops from Iraq quickly.

Defense Department spokesman Bryan Whitman declined to confirm or deny Murtha's claims about what the military investigations have discovered.

Bryan Whitman

"On the recommendation of the investigating officer, a criminal investigation was initiated," he said. "That criminal investigation is still ongoing. Because of that, it would be premature, and in my mind irresponsible, to judge any individuals or units until the investigation is completed."

The spokesman could not say when the second investigation might be completed, but he pledged that if there was wrongdoing the people involved will be punished.

"If somebody has done something wrong, they will be held accountable for those actions," he said.

The unit that was involved in the incident has since returned to the United States. The Marines say three officers who were involved have been relieved of command duties pending the results of the criminal investigation.

U.S. forces are accused of abusing their firepower from time to time, and sometimes the charges are proved. But Whitman said the vast majority of U.S. troops follow the rules, even under the most difficult and dangerous circumstances.

"All of our service-members deployed are held to an extraordinarily high standard of conduct, a standard that is being met every day," he said.

Whitman says the report of the initial investigation will not be made public, at least for now, but he said further information will be made available once the criminal investigation is finished, including any possible indictments of military personnel.