An explosion rocked Baghdad today near the Ministry of the Interior and a plume of smoke could be seen rising above the western part of the capital.
It was not immediately clear what caused the blast.
US soldiers blocked off the site of the explosion, which targeted a passing convoy of American military personnel, witnesses said.
The explosion claimed the life of one US soldier and injured three others.
Helicopters circled overhead, and one took the wounded to a combat hospital.
Several Humvees and Bradley armoured vehicles, as well as a fire truck, were at the roadside site of the blast.
US soldiers and Iraqi police motioned cameramen to turn back.
A series of explosions have shaken Baghdad in the past days, raising fears of more violence ahead of the June 30 transfer of power to Iraqis by the US occupation authority.