The soldier was killed while engaging anti-US forces in Ramadi, west of Baghdad, the US military said on Wednesday.
In the Iraqi capital, five Iraqis were killed and four US contractors were wounded when an explosives-laden car blew up in the path of a US convoy just outside the Green Zone, the heavily guarded district populated by the US embassy and government offices.
Earlier, three separate US convoys were also attacked in other parts of the city, including one near the international airport in western Baghdad, witnesses said.
In one of the blasts, a US military oil tanker was set ablaze in eastern Baghdad, witnesses said.
The truck was hit by a blast at 8.45am (0445 GMT) in a convoy on al-Kanat road, which cuts through eastern Baghdad and borders Sadr City, an Interior Ministry source said.
Surge in violence
Separately, a police source reported an attack on a US military vehicle in the capital's Jadida district, but no further details were immediately available.
In the north of the country, 12 Iraqi guards were killed when a roadside bomb exploded as they were defusing another explosive device, later revealed to be a decoy.
Roadside bombs are the bane of
US military convoys in Iraq
The device detonated on Wednesday near a fuel pipeline in the Badwan area, about 15km north of Kirkuk, Iraqi police sources told Aljazeera.
Kirkuk's chief of police, Major-General Turhan Abd al-Rahman, told Aljazeera that bomb experts were sent to defuse an explosive device found on a road north of Kirkuk.
"The bomb then exploded, killing 12 guards, including two officers, and injuring three Iraqi policemen," he said.
"The killed people do not belong to the Iraqi police. They have been employed with civil contracts. The officers have been granted their ranks by the company overseeing oil installations protection," Abd al-Rahman said.
"Only three policemen were injured on Wednesday. They were at the explosion site to seal off the area and prevent people from approaching it."
Meanwhile, fighting in the western border town of al-Qaim continued for the sixth consecutive day with a US military statement reporting nine fighters killed on Tuesday.
Fighting has been raging in
al-Qaim for the past six days
"During sporadic fighting around Camp Gannon yesterday, nine insurgents were killed by marines," it said in a statement. "All nine insurgents were killed as they attacked the camp with various types of small arms weapons."
The fighting raged 8km east of the border with Syria in al-Qaim-Husaybah region.
On Monday, three US marines and three Iraqis were wounded when car bombs were set off outside the camp.
Sources in the town reported heavy clashes again on Wednesday
Captive's video plea
On Wednesday evening, Aljazeera aired a video tape depicting an American citizen who was taken captive in Iraq on Sunday pleading for the US to work for his release.
The tape on Wednesday showed the US contractor sitting behind a wooden desk as three men pointed their guns at him.
US embassy spokesman in Baghdad Bob Callahan confirmed the captive's name as Jeffrey Ake and said the pictures seemed to be consistent with his appearance, but declined to give further details.
No group has claimed responsibility for the abduction.