Witnesses told Aljazeera at least one Iraqi was killed and five wounded in the fighting in Hiyt on Monday.
A US military spokesman said marines came under fire from about 100 fighters near the town of Hiyt, about 170km west of Baghdad, and engaged in an hour-long firefight.
Some of the fighters took up positions in a mosque, the spokesman in Baghdad said.
"Air strikes were called in on the mosque position. The mosque is partially damaged and is currently on fire," he said.
Hiyt is on the main road that follows the Euphrates river towards Syria.
A US military helicopter was downed in the same city in earlier clashes on Monday, witnesses told Aljazeera.
In the northern city of Mosul on Monday, two Iraqis and a US soldier were killed and 17 others wounded in a car bomb attack against a US military convoy, medical sources and the US military said.
The blast caused a huge crater
A pickup truck sped up alongside the convoy and exploded in Mosul's southern Yarmuk district at 11am (0800 GMT), said Iraqi police First Lieutenant Jar Allah Muhammad Said.
Witnesses said they saw body parts scattered in the street after the blast, which occurred on the main highway leading into the city from the south.
One of the vehicles was badly damaged.
"US forces have closed all roads leading to the explosion site and evacuated the damaged vehicle," Iraqi journalist Muhammad Khalaf said.
US military spokeswoman Captain Angela Bowman said a US-led patrol was involved in a "complex attack", but details were still under investigation.
Two US soldiers were killed and five wounded in a rocket attack in southern Baghdad on Monday morning, a US military statement said.
Fighters and US forces clash
daily in Ramadi
In Ramadi, two Iraqis were killed and three wounded in a firefight between fighters and US marines, medical sources said.
"We have two dead and three wounded," said Dr Hamdi Rawi from the general hospital in Ramadi, west of Baghdad.
US marines and fighters clash daily in the city, where the Iraqi interim government is seeking to impose its authority ahead of elections scheduled for January.
More than 1070 members of the US military have died since US-led forces invaded Iraq in March 2003.
South Korean deployment
Meanwhile, a South Korean air transport contingent was heading to the Gulf to help the country's troops deployed in a Kurdish province of northern Iraq, Seoul's defence ministry said on Monday.
The South Korean contingent is
the third largest in Iraq
The 150-member contingent and four C-130H planes left a military airport south of Seoul for a US air base in Kuwait where they will be stationed from Tuesday, the ministry said.
The air force unit is to airlift supplies and personnel for South Korean soldiers stationed in Iraq, it said.
South Korea deployed about 2800 troops for a relief and rehabilitation mission in Arbil, a Kurdish-controlled town in northern Iraq, last month.
They will be reinforced by another 800 soldiers in November.
The South Korean contingent is the third largest of the US-led forces in Iraq.