A second soldier was injured in the attack near the town about 180km south of Baghdad on Wednesday, said Central Command in a statement.
Small arms fire were fired at their vehicle before they struck another.
The latest death brings to 62 the number of US soldiers killed in resistance attacks in Iraq since US President George Bush declared an end to hostilities on 1 May. Another 62 have been killed in “non-combatant” incidents.
Earlier, a US civilian contractor was also killed and two US soldiers wounded when they came under rocket-propelled grenade (RPG) and small arms fire attack in Tikrit, the hometown of ousted Iraqi President Saddam Hussein.
British soldiers patrol Basra after
the deaths shocked the city
Since US and British tanks rolled into Baghdad on 9 April lawlessness and crimes have been rampant across Iraq.
On Wednesday two children and a woman were killed when a row erupted between traders in the southern Iraqi city of Basra ended in an arson attack on a tanker carrying cooking fuel, which exploded.
Witnesses said the blast occurred at 8pm (16:00 GMT) in the city’s downtown area and sent shockwaves through the British-occupied city.
Two children and a woman standing nearby were killed as the fuel ignited in a fireball. Two other people were injured, including the tanker’s driver, who was severely burned.
A witness said the tanker’s driver had been threatened previously by fuel smugglers because he was selling cooking fuel at a lower price.
Another witness said an unidentified man threw a lit towel at the tanker, setting off the explosion.
Meanwhile, an explosion was heard at the Baghdad Hotel where some members of the US-appointed Iraqi Governing Council were staying, reported our correspondent.
Security officials said a stun grenade was thrown at the hotel, breaking windows but causing no injuries.