Fighting between U.S. forces and Shiite insurgents in the Baghdad slum of Sadr City (search) killed at least 10 people on Thursday, a spokesman for the militants said.

Sheikh Hassan al-Athari, who heads radical Shiite cleric Muqtada al-Sadr's (search) office in the troubled Baghdad district, said five civilians and five militants were killed during "sporadic skirmishes" with American troops. He also said at least 20 people were injured during the skirmishes.

U.S. troops have been fighting with militants loyal to al-Sadr for much of the past two weeks. In recent days, however, the U.S. offensive appeared to have intensified.

Na'eem al-Kaabi, a spokesman for al-Sadr's Mahdi Army (search) militia, said earlier that 50 militants and civilians had been killed on Thursday, but he later said that toll was for the day before and could not be confirmed.

A U.S. official, speaking on condition of anonymity, said Wednesday that 50 militants were killed in recent fighting in the neighborhood.

The Health Ministry said eight civilians were killed and 58 others injured Thursday in Sadr City. Militants often use their own health clinics and do not bring their dead or wounded to state hospitals.

U.S. tanks moved throughout the streets of the slum on Thursday, and helicopter gunships shot at militants from the skies.

U.S. Capt. Brian O'Malley said American troops were carrying out "multiple patrols" in Sadr City. He said fighting erupted Thursday after attackers opened fire on U.S. soldiers patrolling the impoverished district in east Baghdad, which is an al-Sadr stronghold.

"I don't know how many we've killed," he said, adding that several militants had also been arrested.

Associated Press Television News footage showed the streets of Sadr City nearly deserted Thursday as tanks moved through the area. Militants, some with homemade weapons, ran through the streets.

Smoke was seen rising over the area as U.S. armored vehicles, some scarred by gunfire, drove by.

The bodies of two men wearing Iraqi National Guard uniforms were lying dead in the street as a crowd danced around them. Someone then covered the bodies with carpets.

"The tanks and the armored vehicles are besieging Sadr City now," al-Kaabi said, pledging to follow in the footsteps of al-Sadr, whose followers have been fighting with U.S. and Iraqi forces in the holy city of Najaf for two weeks.

"They are killing the innocent civilians just as Saddam did, and their destiny will be shame in this life and the other life," he said.

Two U.S. soldiers were killed in Sadr City during patrols on Wednesday, U.S. officials said Thursday.