Two Marines have been killed in Iraq's western Anbar (search) province "as a result of enemy action," the U.S. military said in a statement Sunday.

The two, both assigned to the 1st Marine Division (search), were injured in separate incidents Saturday. One died the same day; the other died Sunday, the statement said. It provided no other details.

The most populous city in Anbar province, which stretches from Baghdad to the Jordanian border is Fallujah (search), where four American civilians were killed and their bodies mutilated Wednesday.

In the city of Baqouba, 30 miles northeast of Baghdad, a bomb exploded Sunday in the al-Rasool al-Adham Shiite mosque, damaging part of the building, but causing no casualties, said the mosque's caretaker Haider Yassin.

In central Baghdad, hundreds of supporters of radical Shiite Muslim cleric Muqtada al-Sadr rallied in Firdous Square to protest the arrest on Saturday of one his senior aides, Mustafa al-Yaqoubi, in a raid on his house in the city of Najaf.

It was not clear who detained him. U.S. officials could not confirm the arrest and Spanish forces based in the city denied taking action against him.

About 5,000 members of al-Sadr's self-styled militia, the al-Mahdi Army, paraded in Sadr City, a mainly Shiite district in eastern Baghdad, on Saturday. The cleric has been an outspoken critic of the U.S.-led occupation, but has not called for attacks on the occupying forces.

Al-Sadr's weekly newspaper was shut by U.S. officials on March 28, provoking an enormous anti-American outpouring.

On Saturday, gunmen shot and killed the police chief of Mahmoudiya town, 20 miles south of Baghdad, and his driver while they were driving home from the capital.

Not long afterward, six attackers shot at a four-man police patrol in Mahmoudiya, killing one and wounding three, police officer Khaldoon al-Gurairi said. A 60-year-old bystander was also killed.

Guerrillas often target police because they view them as collaborators with the U.S.-led occupation. Also they make easier targets because they are less armed and protected than the U.S. troops.