The marines did not release any other details about the Thursday attack, saying to do so could put other troops at risk.
More than 70 marines died in an offensive to retake Falluja from rebels last month. Fighting is still going on in the city in some areas. Ramadi is in effect held by fighters.
More than 1000 US troops have died in combat since the war in Iraq was launched, while more than 9000 have been wounded, most of them severely.
Bangladeshi driver released
In a separate development, Iraqi captors have released a Bangladeshi truck driver after holding him captive for more than a month.
"Truck driver Abu al-Kashim has been released and he is now in the custody of Iraqi authorities," Bangladesh Foreign Secretary Shamsher Chowdhury said on Friday.
Kashim, 44, was taken captive along with another driver from Sri Lanka while carrying supplies to Iraq from Kuwait on 28 October.
The Sri Lankan driver was also released, an official of Bangladesh's expatriates' welfare and overseas employment ministry said.
Both the drivers were employees of a private Kuwaiti transport company.