In Karbala, American troops sped into the city and seized a government building that also was being occupied by fighters loyal to cleric Muqtada al-Sadr.

A coalition military official said six fighters loyal to al-Sadr were killed in Karbala and one U.S. soldier was wounded in the incursion.

"The city is in our hands," the official told Reuters.

The U.S.-led military coalition and militia loyal to al-Sadr have been in a standoff since al-Sadr's militia took control of parts of Najaf and other Shiite cities south of Baghdad in early April.

The coalition wants to arrest al-Sadr, who is accused of plotting the murder of a rival cleric.

The coalition has moved U.S. troops into the Najaf area. But U.S. officials say they won't launch an offensive to take back the city to avoid a direct confrontation to defeat al-Sadr's forces.

"We're not going to go wading into Najaf; we know how sensitive it is," Brig. Gen. Mark Kimmitt, the military's deputy director of operations, told Reuters.

U.S. officials hope to avoid an armed conflict that could turn Shiite Muslims against the coalition and make al-Sadr a martyr. Moderate Shiites are negotiating with al-Sadr in the hopes of resolving the conflict peacefully.

Soldiers took control of the governor's office in Najaf without a fight after drawing enemy forces out of the city center. But gunfire was heard after they moved in and smoke rose over the city. Motorists fled the area through deserted streets, honking their horns.

Fighters loyal to al-Sadr had controlled the building since April 4.

U.S. officers said the American forces were sent to Kufa, east of Najaf, to draw militia fighters away from the governor's office.

Paul Bremer, the U.S. civilian administrator in Iraq, appointed a new governor for Najaf province and criticized al-Sadr's forces for sowing violence.

"The people of the middle Euphrates are eager for a return to normal life and they're going to have it," he said. "There is no room in the new Iraq for the kind of lawless, self-interested behavior we have seen over recent weeks."

Bremer appointed Adnan al-Zurufi as governor. Al-Zurufi is an exile who participated in the 1991 Shiite revolt after the Gulf War.