The military's call, indicating the possibility of stepped-up military operations, came as Iraqi security forces raided the radio station run by backers of Shiite cleric Muqtada al Sadr and militants launched rockets at a coalition force operating base in the southern port city of Basra, killing two contractors and injuring four civilians and four coalition soldiers.

Sadr City has been a battleground since late March, enduring U.S. airstrikes, militia snipers and gunbattles between U.S. and Iraqi forces and the Mahdi Army, the militia loyal to Sadr.

Already some 8,500 people have been displaced from the sprawling slum of some 2.5 million people, according to the Iraqi Red Crescent. For weeks, food, water and medical shortages have affected about 150,000 people, aid agencies said.

Two soccer fields in east and northeast Baghdad are expected to receive some 16,000 evacuees from the southeast portion of the city where the fighting has been most intense.

Col. Abdul Amir Risna Sigar, the director of sports facilities in Baghdad , said his organization would set up 500 tents around the two fields but are waiting for final orders. The Iraqi Red Crescent was stockpiling food, medical supplies and tents after being informed of the evacuation. It will be responsible for setting up the shelter and living areas for evacuees, the general director, Mazen Saloum , said.

Right now the fields are empty, and families have not come.

Um Mohammed , 48, ignored the Iraqi soldiers calling over loudspeakers for residents to leave their homes on Thursday. Earlier this week the Iraqi army dropped fliers around her home that asked residents to turn over Mahdi Army militiamen and cooperate with the government.

"The residents here are laughing at the government," she said. "Their demands are very strange. Either hand over our sons or leave our houses to live in small tents."

Um Mohammed will stay in her home, she said, even though her neighborhood is beset by gunbattles and sporadic airstrikes.

"We refuse to leave," she said. "Our death will be inside our homes."

In most of Sadr City, people haven't had food rations for more than a month and a half, and the Red Crescent has distributed thousands of food packs, 100 tons of flour and supplied four tons of medical supplies to the two main hospitals. Five hundred to 1,000 people have been killed in more than 40 days of fighting.

The U.S. military also distributed aid and treated citizens for medical conditions as troops continued their battle on the edges of Sadr City.

The U.S. military is putting up barriers to isolate the southern portion of the city, about 2 square miles, where they believe militants are launching rockets into the heavily fortified Green Zone, where Iraqi government offices and the U.S. diplomatic mission are housed. They expect the project to be complete in less than two weeks. The walls will isolate about 800,000 people in the sprawling slum from the rest of the district to stem the flow of rockets and weapons, said Col. Allen Batschelet , the chief of staff of the U.S. military Baghdad command.

"We're putting a series of these barriers that allows us to control access," he said. "Is it disruptive? You bet. Does it slow down commerce? No doubt. But right now that's the cost of reducing the illegal flow of weapons and arms that were getting in there previously."

On Wednesday, Iraqi security forces raided and stopped the broadcast of the Sadrist Al Ahad radio station, radio employees said.

"The army told the manager that the radio station is considered to provoke terrorism," said Akhbal Hameed, a 38-year-old radio employee. "The Iraqi forces blocked, raided and evacuated the building."

Iraqi officials said they didn't shut down the station and only conducted a raid.

(Special correspondents Laith Hammoudi and Jenan Hussein contributed.)