In a statement on Saturday officials said a member of the 1st Marine Expeditionary Force died of wounds sustained during "security and stability operations" in al-Anbar province.
The death raised the US toll in Iraq since the beginning of the war to 903, according to news agencies.
It was not immediately clear where in the province the dead marine had been fighting when he was injured.
It is unclear how many Iraqi casualties were sustained.
But marines and Iraqi resistance fighters fought daylong clashes on Wednesday in the town of Ramadi, 112km west of Baghdad.
In the central city of Samarra, two Iraqis were killed and two others injured in an explosion in the Jubairiya district. No further details were immediately available, Aljazeera's correspondent said.
Also on Saturday, Iraqi security sources told Aljazeera that oil pipelines between the Biji and Dura refinery were targeted as an explosive device struck the Tharthar area in Samarra.
Plumes of smoke were seen rising from the site of the explosion according to witnesses.