"Four Soldiers assigned to First Marine Expeditionary Force were killed in action March 4, while conducting security and stability operations in Anbar province," the statement said on Saturday without providing further details.
A separate statement said one US soldier was killed and another wounded in a vehicle accident near Tikrit, north of Baghdad, at about 10pm (1900 GMT) on Friday.
The latest deaths raised to 1499 the number of US servicemen killed in attacks or accidents in Iraq since the launch of the US-led war nearly two years ago, according to Pentagon figures.
Separately, five Iraqi soldiers were killed overnight on Saturday in a mortar attack on their base near Duluiya, north of Baghdad, said an Iraqi army officer.
The attack happened at about 3am (0000 GMT) as new army recruits were training, said Captain Asaad Saddad.
Meanwhile, Iraqi police in the city of Samarra, 120km north of Baghdad, imposed a curfew from 7am (0400 GMT) to 9pm (1800 GMT) as it sought to prevent an anti-American
demonstration called for by the local chapter of Association of Muslim Scholars, according to resigning mayor Taha al-Handira.
The mayor had quit in protest against what he saw as restrictive and tough security measures imposed by US and Iraqi forces on the city.
Samarra was the scene of a
US-led assault in October
Iraq recently renewed a state of emergency countrywide, except for the Kurdistan region, for 30 days.
In a separate development, the Iraqi army arrested 17 suspects, including a former senior member of the disbanded Baath Party in Kirkuk, northern Iraq.
The army said in a statement on Friday that the arrests, which were carried out in collaboration with the US troops, were made in al-Nasiriya, al-Asiriya and al-Tariqiya villages, south of Kirkuk.
The statement noted that among the arrested suspects was Madhi Nasir al-Ubaidy, a close associate of former Iraqi vice president Izzat Ibrahim al-Duri.