The Marines were assigned to the 1st Marine Expeditionary Force, which is responsible for security in a wide area from just west of Baghdad to the borders of Syria and Jordan. The statement gave no further details, citing security.
Earlier Saturday, Iraqi witnesses reported attacks on military convoys near two towns in Anbar province - Fallujah and Ramadi - and a large explosion in the area of Fallujah after sundown. However, it was not known whether the Marines died in any of those incidents.
Also Saturday, the U.S. military reported two other service member deaths - one soldier from the Stryker Brigade who died Friday from non-hostile causes in northern Iraq and the other soldier from the 81st Brigade Combat Team who was killed Tuesday in a mortar attack south of Baghdad.
In the south, the U.S.-appointed governor of Najaf accused radical cleric Muqtada al-Sadr on Saturday of failing to honor a deal to end the fighting in the holy city of Kufa. This, as U.S. soldiers clashed with Shiite gunmen in Kufa for the second straight day since the agreement was announced.
Al-Sadr's fighters said they killed one Iraqi policeman and captured another during an exchange of fire in Najaf's twin city Kufa.
Three Iraqis were injured in clashes Saturday in Kufa, hospital officials said. There were no reports of any U.S. casualties.
In other developments:
As of Friday, 800 U.S. service members have died since the beginning of military operations in Iraq last year, according to the Defense Department. Of those, 585 died as a result of hostile action and 215 died of non-hostile causes.
It was unclear whether the latest Defense Department tally included any of the deaths reported Saturday.
Najaf Gov. Adnan al-Zurufi complained al-Sadr had done little to stop his fighters from brandishing their weapons in public or to send militiamen who are not from this city back home - key parts of the agreement he struck with Shiite leaders to end seven weeks of fierce fighting around Najaf and Kufa.
"Unfortunately, there have been no positive initiatives from the office of Mr. Muqtada al-Sadr so far," al-Zurufi told reporters. "Armed men are filling the streets and there have been number of attacks on state employees in Kufa."
Ragtag fighters wielding Kalashnikovs and rocket-propelled grenades exchanged fire with U.S. soldiers approaching the center of Kufa. The militia accused the Americans of shooting first. Coalition officials said U.S. soldiers were attacked by rocket propelled grenades and fired back.
Neither side released any casualty figures. Al-Sadr's militia said they killed one Iraqi policeman and captured another during a clash between Najaf and Kufa.
"God has protected us because truth is on our side," said one fighter, Salam Abdel-Aali. "Truth is in our side. Truth is always victorious."
Explosions could be heard in the center of Kufa, where al-Sadr's fighters had taken up positions in the streets surrounding a mosque. Militiamen manned checkpoints, standing near concrete barriers including one with a graffiti that read "Yes to armed resistance!"
In Kufa's Furat al-Awsat hospital, Ali Moussa, 22, lay in a hospital bed with shrapnel wounds. His head was wrapped in a bandage and his black T-shirt was soaked in blood. Moussa would not say if he was a member of the al-Mahdi Army.
"I was walking down the street and they started attacking people," he said of the Americans. "They say there is a truce. Where is this truce?"
The deal announced Thursday provides for an end to armed clashes and with removal of al-Mahdi militia fighters from the streets. It also calls for discussions between al-Sadr and the Shiite political and clerical hierarchy over the future of the al-Mahdi Army as well as the status of an arrest warrant charging the young cleric with murder in the April 2003 death of a moderate cleric.
That affords al-Sadr a way out of his problems despite U.S. claims that it would kill or capture him to put an end to his militia, which represents a challenge not only to the coalition but to Shiite leaders whom Washington has cultivated.
The agreement makes it unlikely that al-Sadr will have to face justice or disband his militia before the Americans return power to the Iraqis on June 30.
The coalition has said it was not a party to the agreement but would suspend offensive operations to give the deal a chance to bring peace to this city, revered by Shiite Muslims worldwide.
In a statement Saturday, an official the country's largest Shiite political party - the Supreme Council for the Islamic Revolution in Iraq - blamed al-Sadr fighters for the continuing violence and for an assassination attempt against one of its officials, Sadreddine al-Qobanji. Al-Sadr's office has denied the allegation.
An attacker opened fire Friday on al-Qobanji after he led prayers at the Imam Ali mosque, according to the cleric's spokesman Qasim al-Hashemi.
"As we condemn this terrorist act, we believe that elements of the al Mahdi Army are primarily responsible for what happened," said al-Hashemi.
The assailant was arrested by al-Sadr militiamen but they would not hand him over to SCIRI, al-Hashemi said. "This means that this person is one of them, and is associated with them."