"A Task Force Lightning soldier assigned to 3rd Brigade Combat Team, 1st Cavalry Division, was injured on Thursday as a result of enemy action in Diyala province," a statement said.
"The soldier was transported to a coalition forces medical treatment facility and later died of wounds," it added.
The military gave no details of how the soldier was wounded, but his unit had previously been reported to have gone into action on Thursday in Diyala to rescue a unit of Iraqi police that had been ambushed by insurgents.
At least 24 police and 18 rebels were killed in the battle, one of the fiercest in recent weeks in a region known as a hunting ground for insurgents and a hotbed of sectarian violence.
At least 2,803 members of US forces have now been killed or died accidentally in the Iraq campaign since the March 2003 invasion, according to an AFP count based on Pentagon figures.

Copyright AFP (Agence France-Presse), 2006