WASHINGTON (CNN)  -- Several Marines who were involved in the November 2004 offensive in Falluja, Iraq, are now the focus of an investigation into allegations that civilians were intentionally killed during the operation, several Pentagon officials have confirmed.



Members of the 1st U.S. Marines Expeditionary Force operate in Falluja, Iraq, in November of 2006.



No one has been charged in the probe, which is based on what one official told CNN were "credible allegations" from a former Marine. That Marine volunteered the information during an employment polygraph test administered by the U.S. Secret Service.



Several sources familiar with the probe say the Naval Criminal Investigative Service is conducting the investigation.



The allegations first surfaced on a Web site, defendourmarines.com, posted by Nathaniel Helms, a military journalist who wrote a book about the Marines in Falluja.



The Web posting includes an account from a Marine who alleges eight captured Iraqis were gunned down following a firefight.



The weeklong anti-insurgent offensive in Falluja began on November 7, 2004. It was called Operation New Dawn, and it sparked intense fighting involving airstrikes and house-to-house searches. There were reports of civilians being killed in the crossfire at that time.



The allegations are the latest involving Marines and civilian deaths in Iraq. Seven Marines and a Navy medic were charged with killing an Iraqi civilian in Hamdaniya in April 2006. One Marine will serve eight years in a plea deal; another Marine withdrew his guilty plea, saying he acted under orders.



Four Marines were charged with murder in the 2005 killings of 24 Iraqi civilians in Haditha. Four officers are accused of failing to investigate and report the deaths properly. Haditha was a target of Marine operations to root out insurgents.



Both U.S. military law and international law of armed conflict prohibit the killing of unarmed captured prisoners, whether or not they are combatants.  E-mail to a friend
Who are the focus of the 2004 Falluja civilian death investigation? Who is conducting the probe? what caused the marines to be the focus?
Several Marines Naval Criminal Investigative Service allegations that civilians were intentionally killed during the operation,
question: Who are the focus of the 2004 Falluja civilian death investigation?, answer: Several Marines | question: Who is conducting the probe?, answer: Naval Criminal Investigative Service | question: what caused the marines to be the focus?, answer: allegations that civilians were intentionally killed during the operation,