U.S. troops and Shiite Muslim guerrillas fought Friday morning in the southern city of Kufa, but American officials said the combat did not qualify as a significant breach of a day-old cease-fire with forces loyal to rebel cleric Moqtada Sadr.

Hospitals reported that three Iraqis were killed in the fighting, which began as U.S. forces entered Kufa on patrol and were ambushed by fighters with AK-47 assault rifles and rocket-propelled grenade launchers. Insurgents also attacked U.S. soldiers directing traffic on a road east of the city and a reconnaissance patrol outside a military base and fired mortar rounds at that installation. Two soldiers were wounded in the fighting, U.S. officials said.

Brig. Gen. Mark Kimmitt, the chief U.S. military spokesman in Iraq, said the incidents "would appear to be violations" of the deal reached Thursday to end fighting in the south. However, Daniel Senor, spokesman for the U.S.-led occupation authority, said the fighting was not cause for revoking the military's pledge to halt offensive operations against the insurgents. "The macro trend continues to be positive," he said.

Armored U.S. forces and RPG-wielding Shiite guerrillas have battled for weeks in Kufa, Najaf and other southern cities, and turmoil has occasionally erupted in Sadr City, the vast Baghdad slum where Sadr enjoys significant support. With the scheduled transfer of limited power to an Iraqi government just five weeks away, U.S. officials consider stability in the south, home to most of the Shiites who make up a majority of Iraq's population, as fundamental to any chance of a peaceful transition.

Under the deal struck Thursday, Sadr was supposed to pull his forces off the streets of Kufa and the nearby city of Najaf and withdraw fighters not resident in those cities. In return, U.S. demands that he disband his Mahdi Army militia and surrender on charges of murdering a moderate Shiite cleric last year were put on hold. At some unspecified time in the future, Shiite political leaders are supposed to negotiate Sadr's future with him.

As he did Thursday, Senor took pains to emphasize that "Moqtada al-Sadr must disband and dissolve his illegal militia and submit himself to justice." The cease-fire, he added, "is just a first step."

The fighting Friday in Kufa was evidence of the threat that the Mahdi Army will continue to pose until its status is resolved.

Sadr's guerrillas, suspicious that U.S. troops were entering Kufa to apprehend him on his way to Friday prayers at the city's main mosque, took to the streets, witnesses said. Sadr did not preach, and when word spread to Najaf, the guerrillas took up positions in the city's cemetery, where they hid among the sarcophagi and tombstones. They also set up checkpoints near the Imam Ali shrine, which is Najaf's main mosque and one of the holiest sites in Shiite Islam.

Meanwhile, U.S. troops pushed deep into Sadr City, where mosques canceled Friday prayers as religious leaders flocked to Kufa to show support for Sadr. As Bradley Fighting Vehicles rumbled through trash-covered streets, they passed by a banner that read: "Welcome U.S. Army in a second Vietnam."

After prayers in Najaf, a gunman ambushed a car carrying Sadr Eddine Qubanshi, a cleric and an official of the Supreme Council for the Islamic Revolution in Iraq, a Shiite political party that has been cooperating with the occupation authority and mediating Sadr's cease-fire. The ambush took place just outside the walls of the Imam Ali shrine.

Qubanshi escaped unharmed, but suspicions immediately fell on the Mahdi Army. Some of its fighters then began to blame other Shiite groups for the attack, on the grounds that they were trying to incite a Shiite civil war.

In the western city of Fallujah, where a recent deal with Sunni Muslim insurgents also produced inconclusive results, four members of an NBC television crew were freed by kidnappers who had held them for four days.

The four -- correspondent Ned Colt, cameraman Maurice Roper, sound man Robert Colville and Iraqi freelancer Ashraf Taie -- "were released Friday morning Iraqi time, with the assistance of local leaders, after their identification as journalists became clear," NBC News said in a statement.

A statement from the 1st Marine Expeditionary Force, based outside Fallujah, said the Marines had advised the crew not to venture into Fallujah. "The crew's decision to enter the city was irresponsible," the statement said. In effect, U.S. officials acknowledged that Fallujah remains far from pacified. "Quiet," said Kimmitt, "does not mean peace."

Guerrillas from Fallujah have filtered into other cities around Baghdad, U.S. officials say, and are especially menacing where the road south from the capital passes through hamlets populated by Sunnis before it heads into the Shiite heartland. "There's spillover from Fallujah there," Kimmitt said.

On Thursday, gunmen sprayed automatic fire at a car carrying Japanese journalists along that road 20 miles south of Baghdad. The car burst into flames, and two of the journalists died.

Correspondent Scott Wilson in Baghdad and special correspondent Saad Sarhan in Najaf contributed to this report.