Four U.S. soldiers were killed and five wounded Friday when their vehicle was blown up in the Iraqi capital, Baghdad.

U.S. military officials say the attack came as American forces clashed with militiamen loyal to radical Shi'ite cleric Moqtada al-Sadr.

The fighting broke out earlier Friday when insurgents fired mortar rounds and rocket-propelled grenades at a police station in the mainly Shi'ite Baghdad district of Sadr City. At least three Iraqis were killed.

Also in Baghdad, the U.S. military says Iraqi police have detained a known terrorist and murder suspect, Umar Baziyani, who is an associate of terrorist leader Abu Musab al-Zarqawi. Zarqawi is wanted in the beheading of American civilian Nicholas Berg.

Meanwhile, efforts continue to end daily clashes between U.S. troops and Moqtada al-Sadr's militiamen around the Shi'ite holy cities of Najaf and Kufa.

A U.S. military official, Colonel Brad May, said American troops will pull back from positions near holy sites and Iraqi police will move in to secure the cities.

Moqtada al-Sadr did not turn up to deliver his Friday sermon in Kufa. Instead he sent an aide to read a a statement dismissing the new Iraqi interim government as unacceptable because, in his words, it was appointed by the "occupier."

In New York Thursday, Iraq's new foreign minister Hoshyar Zebari urged Security Council members to give the interim government full sovereignty, along with a voice in deciding how long foreign troops remain in the country and how they operate.