An Iraqi security official says a roadside bomb has exploded north of Baghdad, killing eight fighters from a militia headed by an influential Shiite Muslim cleric.

Thursday's ambush was confirmed by a spokesman with the Peace Brigades, or Saraya al-Salam militia, which is commanded by Muqtada al-Sadr. They both spoke on condition of anonymity because they were not authorized to speak to the media. The militia spokesman said among those killed was a militia commander, Hussein Attiyeh.

The ambush occurred west of the holy city of Samarra, some 60 miles (96 kilometers) north of the capital Baghdad.

There was no immediate claim of responsibility for the attack. Al-Sadr's political coalition came first in last year's May elections.