The U.S. military said the assault took place in the province of Salah Al-Din, a Sunni militant stronghold north of Baghdad.
It says U.S. soldiers came under heavy fire while investigating intelligence reports that Al-Qaeda-linked militants were operating in the area.
The statement said U.S. troops later found multiple weapons caches.
In southern Iraq, more than 1,000 British and Danish troops stormed a suburb of Al-Basrah today and arrested five militia leaders accused of carrying out attacks against coalition forces.
A spokesman for the British military said it was the biggest operation of its kind since 2003.
Meanwhile, the U.S. military said one of its soldiers was killed on December 7 by a roadside bomb in Baghdad. That raises to 33 the number of American forces who have died in Iraq in the first week of December.
(Reuters, AFP, AP)