One of Shiite Islam's most sacred sites, the Imam Ali shrine in Najaf, sustained minor damage today when it was hit by rockets or mortars from an unknown source. The top U.S. military spokesman in Iraq denied that U.S. forces were responsible.

Residents of Najaf, a Shiite holy city about 90 miles south of Baghdad, said the shrine to Ali was struck by unidentified projectiles, damaging an inner gate of the shrine and slightly injuring at least three people, news agencies reported. Shiites, who make up the majority of Iraq's population, regard Ali, the son-in-law of the prophet Muhammad, as the prophet's rightful heir and greatly revere his burial place.

Supporters of Moqtada Sadr, a radical young Shiite cleric whose militia has been fighting forces of the U.S.-led occupying coalition in Iraq, blamed the United States for the damage and claimed that a dozen people had been injured. The supporters said at least one projectile hit the inner gate, which leads to Ali's tomb, and that another landed outside the shrine about 10 yards from an outer wall.

But in a news conference in Baghdad, Brig. Gen. Mark Kimmitt said that "coalition forces had no involvement in the damage to the Imam Ali mosque." He had said earlier that the projectile that hit the shrine was not American and not fired by coalition forces.

Kimmitt told reporters that he had heard different accounts of the attack, including one that attributed it to fighting between two rival Iraqi factions. Another version, he said, was that Sadr's militia, the Mahdi Army, had fired on the mosque from a cemetery to "try to provoke outrage so they could blame it on the coalition forces."

He said U.S. forces "are trying to handle the situation right now" in Najaf. "On behalf of the entire coalition, we just can't tell you how much we decry the attempts by Moqtada's militia -- Moqtada possibly himself -- to violate the sacred holy shrines of the [Shiite] religion for his own personal gain," Kimmitt said.

"We don't want to see that. We'll do what we can to prevent it. We certainly will not allow that to go unanswered, but nor will we be provoked into an incident near those shrines which might have the same outcome."

Kimmitt said Sadr's militia has continued to attack U.S. forces at Najaf and the neighboring town of Kufa, firing dozens of mortar rounds during the past 24 hours but causing no significant damage or casualties. He said U.S. troops yesterday killed a forward observer for the militia who was directing mortar fire near Kufa.

At the same time, Kimmitt said, U.S. commanders are optimistic about developments in Karbala, another Shiite holy city. He said Sadr's militia reportedly has moved out of the city, and he suggested that reporters ask residents how the militiamen had treated them. In Karbala, he said, "the coalition forces showed great respect for the shrines, where Moqtada's people did not."

In other developments in Iraq, a suicide car bomb blew up near a hotel in central Baghdad, killing the bomber and slightly injuring two other people, Kimmitt said. The bomber's target was not immediately clear, but observers noted that it was about 100 yards away from the Australian Embassy.

Kimmitt said one U.S. soldier later suffered minor wounds when attackers fired two or three rocket-propelled grenades toward an Iraqi police station in central Baghdad, apparently from a nearby apartment building. Iraqi authorities said the weapons were rockets.

Police subsequently raided the building and came out with a homemade platform for launching rockets, the Reuters news agency reported.