KARBALA, Iraq - Heavy gunfire and huge explosions resounded today as American forces battled Iraqi militiamen near a gold-domed shrine that is one of the most sacred sites for Shiite Muslims. Thick smoke rose over the city center.

In Karbala, fighters loyal to radical cleric Muqtada al-Sadr regrouped in alleys north of Imam Hussein shrine.

Fighting also raged near the city's Imam Abbas shrine. American forces are concerned that any damage to the two shrines could enrage Iraq's majority Shiite population as the United States tries to stabilize Iraq ahead of a transition to sovereignty on June 30.

Residents said the fighting, which began Tuesday night, left many homes destroyed and shops gutted by fire, and many families fled to safer areas of the city. In some cases, men stayed while women and children left.

Young men gathered at some street corners to watch the fighting. Militiamen in groups of three and four moved in side streets.

Pilgrims pleaded with guards of the two shrines to let them in, but they remained closed.

The U.S. military said a soldier was killed when a roadside bomb exploded beside his military convoy in Baghdad on Wednesday, and a U.S. Marine died of wounds suffered during security operations in western Anbar province on the same day.

On Wednesday night, al-Sadr followers stormed three police stations in Najaf, killing one policemen and injuring two. The attackers looted several cars and some weapons, and destroyed computers and furniture, said Brig. Hassan Hamza, deputy police chief.

U.S. soldiers later arrived and retook the police stations.

Hospital officials in Najaf said four people were killed and six injured in overnight fighting between American forces and al-Sadr supporters.

Dozens of Iraqi police with assault rifles took up positions behind concrete barriers on the southern approaches to Karbala, possibly to prevent reinforcements from arriving to help militiamen in the city.

U.S. tanks, helicopters and jets attacked al-Sadr's fighters in Karbala on Wednesday, partially destroying a mosque that insurgents had used as a base. American forces killed 22 militants, Brig. Gen. Mark Kimmitt said in Baghdad.