In other attacks on Monday, fighters fired mortars and shot at polling stations at two different locations, killing a security guard and engaging US troops protecting a school designated for voting.
In Ramadi, three Iraqi civilians were killed and nine others injured on Monday during clashes, Aljazeera learned.
The clashes erupted after a car bomb targeting a US military patrol exploded, injuring some soldiers. There was no immediate confirmation on any US casualties.
The US military headquarters also came under gunfire and the atmosphere in Ramadi was tense.
US soldiers killed
Two US soldiers were also killed on Monday in al-Anbar province in western Iraq, the military said.
It said both soldiers came from the 1st Marine Expeditionary Force and died while "conducting security and stability operations".
Details on the circumstances of the deaths was not provided, but the deaths may be connected to the Ramadi car bomb attack.
Near Baquba, another stronghold of anti-interim government fighters, fighters opened fire at a checkpoint and killed eight Iraqi soldiers, an Iraqi National Guard officer said.
Polling stations attacked
Clashes erupted in the southern town of Musayib after fighters opened fire on a polling station. One guard was killed and two others were wounded. One of attackers was also wounded, police said.
US troops are racing against time
to boost security before the polls
In the troubled northern city of Mosul, mortars were fired at a school that will serve as a polling station, and US troops guarding it returned fire.
The latest violence came as the clock ticked down to the planned 30 January polls to elect a 275-member national assembly.
Police in Basra, Iraq's second-largest city, said mortars were fired overnight at three schools in the city that will be used as voting centres. They said nobody was wounded.
About 650 additional British troops have arrived in Basra to help maintain security for the polls, a British military official said on Monday.
Iraqi interim Prime Minister Iyad Allawi and the US government insist the elections should go ahead, although they concede some areas may be too unsafe for voting.
The interim government says it is preparing a range of measures to protect voting stations.
The authorities said on Monday that the army had killed "35 insurgents and arrested 64 others" in clashes west of Baghdad in recent days.