According to the US military, the soldiers were travelling in a convoy near Tall Afar, about 400km northwest of Baghdad, when the bomb exploded.
One soldier died while being taken to a nearby hospital by helicopter, the military said.
Soldiers in the convoy fired on several attackers after the explosion, but were unable to capture anyone, the military said.
The latest death brings to about 376 the number of US soldiers killed in action in Iraq since the US-led invasion last March which toppled Saddam Hussein.
Also on Monday, two US soldiers died in separate attacks on convoys in central and north Baghdad.
In the first incident, a US soldier was killed and another wounded after their convoy was hit by a roadside bomb in central Baghdad.
A US military spokesman told Reuters the explosion took place at 9.20 am (0620 GMT). He gave no further details.
Just over one hour later, another US soldier was killed and four Iraqis wounded by the explosion of a home-made bomb targeting a US military convoy in the town of Baquba, 60km north of Baghdad, Iraqi police said.
At least 376 US soldiers have now
been killed since the invasion
"The blast took place near the Al-Rahma hospital at 10:30 am (0730 GMT) when an American military convoy passed by," Lieutenant Majid Muhammad told AFP.
"Four street peddlers were wounded," he said.
"The convoy was passing when the bomb went off. I saw the doors of a military vehicle fly up in the air," said Suhail Khudayir, a 50-year-old peddler who was injured together with his two teenage boys.
A US military spokesman said US soldiers and Iraqi police searched the area and captured two men suspected of involvement in the blast.
"One of the individuals had a cell phone and we are trying to determine if it was used to detonate the bomb," the spokesman said.
At least one child was killed and four others wounded in an explosion at a primary school in the Iraqi capital.
Brigadier-General Mark Kimmitt, the chief US military spokesman, told a news conference two people were killed and three wounded by a bomb. Their ages were not clear.
School children were visibly
shaken by the explosion
AP reports police and hospital sources said earlier one child was killed and one was wounded when a grenade in a garbage can exploded as they played near the school.
The grenade had apparently been dumped in the bin and was detonated by the children as they played close to Al-Jawadain school in the Khadimiya district of northwestern Baghdad. 'Intentional'
A Baghdad police official, Colonel Adnan Abd Al-Rahman, said the blast was intentional, but that only one child was killed.
Police sergeant Abd al-Amir Hamid had told reporters at the scene the explosion was accidental, caused by an old grenade left in a corner of the school's playground.
"The grenade, which seems to have been there for a long time, exploded when students started a fire in a trash bin" in a corner of the schoolyard
Abd al-Amir Hamid,
"The grenade, which seems to have been there for a long time, exploded when students started a fire in a trash bin" in a corner of the schoolyard, he said.
A series of powerful blasts have targeted Iraq's Shia majority, as well as the rival Sunni Muslim community, in what many US and Iraqi officials suspect is a plot by foreign fighters and old regime loyalists to provoke a civil war.
US forces have arrested the mayor of Falluja, one of eight local officials who quit, a day after a bloody raid in the Iraqi town.
According to Issa al-Aday, deputy head of Falluja's council, US soldiers arrested Raied Husayn Brisha on Sunday, the day he handed in his resignation after receiving numerous death threats. It was not clear why Brisha was arrested.
Attackers used RPGs in the
Al-Aday said the US forces detained him because he did not have their permission to quit. The US military had no immediate comment.
Four other city councillors and three of the city's 45-member governing council also resigned on Sunday, al-Aday said.
Brisha's office was one of those hit when scores of gunmen stormed a police station and two other government buildings in Falluja on Saturday. The attack in the city, 50km west of Baghdad, killed 22 police and a civilian.
Dozens of prisoners held in the police station escaped during the battle and police killed four attackers.
Al-Aday said elections on Thursday would choose Brisha's successor.