There has been an explosion in the northern Iraqi city of Tikrit, where a bomb went off inside a car, killing two Iraqis.
Another Iraqi man in the vehicle was seriously injured.
The Americans said it appeared that the men had been planning to attack a US patrol, but their bomb had gone off prematurely.
A military spokesman, Lieutenant Colonel Steve Russell, said the car - a white Mercedes - was believed to have been used in previous attacks against the US-led coalition forces, including one in December in which three American soldiers were wounded.
One report says one of the men killed was a relative of the former Iraqi leader, Saddam Hussein.
In another incident, in the south of the country, two British soldiers in Basra received minor injuries when a small roadside bomb exploded as their patrol was passing.
From the Newsroom of the BBC World Service.