BAGHDAD (AP) _ U.S. forces on a raid in northern Baghdad killed a Shiite militant believed to have masterminded a brazen January attack in Karbala that led to the capture and killing of four U.S. soldiers, the military said Sunday.

Troops located Azhar al-Dulaimi on Friday morning and tried to capture him, but he was killed in the ensuing battle, Maj. Gen. William Caldwell, the spokesman for U.S.-led forces in Iraq, said on CNN's ``Late Edition.''

U.S. troops had been pursuing al-Dulaimi relentlessly since the Jan. 20 attack in the southern city of Karbala, Caldwell said.

In that attack, gunmen speaking English, wearing U.S. military uniforms and carrying American weapons attacked a joint military command headquarters where U.S. military officers and their Iraqi counterparts were meeting.

The attackers killed one soldier and abducted four others, whom they later shot to death.

``You know, anybody who kidnaps an American soldier and murders them, we're going to continue to hunt down. And that's exactly what we've been doing with this guy,'' Caldwell said of al-Dulaimi.

Thousands of U.S. and Iraqi soldiers are still searching for three American troops who were captured in an ambush south of Baghdad last week.

Caldwell said the military would not abandon the search for the missing soldiers.

``We're not going to give up on our soldiers. We have every reason to believe at this point still that they probably are alive,'' he told CNN. ``There's nothing to indicate otherwise. And so we're going to continue what we're doing.''