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Prime Minister Nouri al-Maliki gave Shiite Muslim militiamen in Basra three days to surrender as fighting raged Wednesday in the southern Shiite heartland and parts of Baghdad, leaving more than 80 people dead since the previous day.

Basra residents trapped in their homes by gun battles worried that food was running out with no end in sight to the clashes between Iraqi security forces, followers of Shiite cleric Moqtada Sadr and other factions.

Volleys of rocket and mortar fire shook the capital Wednesday, including the fortified Green Zone that houses the U.S. Embassy and Iraqi government offices. One U.S. soldier, two American civilians and an Iraqi soldier were wounded in the attacks, the military said.

Two U.S. soldiers were killed by hostile fire in separate attacks Wednesday in Baghdad, the military said. The deaths lifted to at least 4,003 the number of American military personnel killed in the war, according to an Associated Press count.

Fighting erupted Tuesday in Basra when Iraqi government security forces announced the launch of a crackdown against armed factions and criminal gangs that are vying for control of the city and its lucrative oil industry. By Wednesday, more than 30 people had been killed and 100 injured in Iraq’s second-largest city, health officials said.

The resistance represented a major challenge to al-Maliki’s authority and deepened fears that a cease-fire declared last year by Sadr may collapse.

Sadr’s followers have complained for months that U.S. and Iraqi security forces, many of them with ties to rival Shiite factions within the government, are taking advantage of the truce to arrest members of Sadr’s Mahdi Army militia and weaken his movement before provincial elections scheduled for Oct. 1. Sadr’s representatives called Tuesday for protests.

The unrest quickly spread to Kut, Hillah and several neighborhoods of Baghdad, where small groups of demonstrators took to the streets and Mahdi Army members traded gunfire with U.S. and Iraqi security forces and rival militias. Late Wednesday, explosions could also be heard in the city of Najaf.

A statement from al-Maliki, who is overseeing the campaign from Basra, gave gunmen 72 hours to turn themselves in, surrender their weapons and sign a written pledge renouncing violence or face what he termed serious penalties.

Sadr issued no comment. But officials at his Najaf headquarters said the cleric is urging followers to respect the truce and would send representatives to Basra to talk with local leaders.

At the same time, Liwa Sumeysim, who heads Sadr’s political operations nationwide, said al-Maliki’s presence and the deployment of 3,500 extra police and soldiers to Basra were a provocation and they should leave.

U.S. officials in Washington voiced approval Wednesday for the offensive, which comes just two weeks before Army Gen. David Petraeus, the overall commander in Iraq, is due to present recommendations for Iraq strategy to Congress.

Stephen Hadley, President Bush’s national security adviser, said the offensive is aimed at militia members who have continued to fight in spite of Sadr’s orders.

“It’s not a move, as we read it, by the central government to repudiate the cease-fire in any way,” Hadley said.