Clashes between U.S.-led forces and fighters loyal to Shiite Muslim cleric Moqtada Sadr continued for a third day in the holy city of Najaf and the large Shiite slum in Baghdad called Sadr City, where gunmen set up illegal checkpoints and ran openly through the streets with weapons.

Officials at three hospitals in Najaf said 23 civilians were killed and 121 wounded in the day's fighting, which subsided at night. It was the fiercest combat in months and posed a daunting challenge to Iraq's interim government as it struggles to bring stability to a country wracked by a violent, persistent insurgency.

As part of a plan to defuse the situation, Prime Minister Ayad Allawi on Saturday offered amnesty to insurgents who turn in their weapons and provide information to local police. The amnesty program, which Allawi had promised since taking office on June 28, will last 30 days and will not apply to those suspected of major crimes such as murder, rape and destruction of property. It also does not apply to people already in custody.

In another development, the interim government closed the Baghdad offices of Arab satellite network al-Jazeera for a month, banning it for allegedly inciting violence.

On Saturday night, nearly a dozen bombs exploded in the center of the capital near the fortified compound that houses the interim government and the U.S. Embassy. Such late-night explosions have become more frequent in recent days; two hotels in Baghdad housing foreign journalists and contract workers were attacked Thursday and Friday nights. No one was injured.

In Najaf, an uneasy calm settled over the city after dark. Members of Sadr's militia left the vast Wadi al-Salam cemetery, where they had taken up positions during the last three days to launch rockets and grenades. The Marines, who had been fighting the militants along with the Iraqi police and National Guard, said large caches of weapons, including rocket-propelled grenades and explosive-making materials, were found in the cemetery.

The Marines said Sadr's militia had used the cemetery as an operating base, violating the conditions of a truce negotiated in June after a two-month uprising that left hundreds dead.

The militia, known as the Mahdi Army, "kidnapped their enemies, including innocent civilians, bringing them to the cemetery for torture, execution and burial," the U.S. military said in a statement.

Ghalib Hashim Jazaeri, Najaf's chief of police, said Iraqi security forces staged an unsuccessful raid on Sadr's home in Najaf on Saturday, the Los Angeles Times reported. "We surrounded the house, but he was not at home," he said.

U.S. and Iraqi security forces said fighting broke out on Thursday after members of the militia attacked an Iraqi police station. As the Iraqi forces asked for help from the Marines, the violence escalated rapidly, spreading to other cities in the south and to Sadr City in the capital.

Through his associates, Sadr called on his militia to rise up against the U.S. military and its allies. Insurgents responded, taking to the streets and battling coalition forces.

It was not clear whether the fighting had ended in Najaf on Saturday night or would resume at daybreak. The streets were virtually empty as the sun went down, except for a group of gunmen who chanted Sadr's name as they rode around in the back of a U.S. military truck that they apparently had seized. The city had no electricity or power, and a large market in the center of the city was burned to the ground.

The U.S. military said Friday that more than 300 militant fighters were killed in the first two days of clashes. A spokesman for Sadr in Baghdad denied the claim.

Allawi said Iraqi security forces arrested more than 1,200 people in connection with the fighting. He said the military operations were not aimed at Sadr or his followers and that he did not believe the insurgents were members of Sadr's Mahdi Army -- a statement that angered some of Sadr's top associates.

"We think these are gangs, and they use his name as cover," Allawi, a Shiite, said at a news conference. "I have been receiving positive messages from Sadr. That is why we don't think the people that are committing the crimes in Najaf and elsewhere are his people."

Ahmed Shaibani, Sadr's spokesman in Najaf, denounced Allawi, saying if he were a true Shiite Muslim, he would not participate in the U.S.-backed interim government. "He should support the Islamic resistance whether it is Sadr or another resistance," Shaibani said in a telephone interview. "He is the prime minister of an Islamic country."

A group of influential Shiite political leaders also lashed out at Allawi and the interim government for not backing Sadr and his militants. Members of the Shiite Political Council, formed three months ago to represent 38 political parties, urged the government not to respond to the militia forces with violence.

"We ask the government not to lose its balance when facing the incidents in Najaf city," said Abdul Karim Muhammadawi, a former member of the now-disbanded Governing Council, and current member of the Shiite political group. "We tell the government that this case should be solved through political solution not military."

Ali Yassiri, Sadr's political coordinator in Baghdad, said the interim government should negotiate for peace. "It has been three days now of abusing human rights," he said. "A huge terrorist activity is being imposed on Najaf City and Sadr City. We put responsibility on the U.S. government and occupation and the governor of Najaf," who ordered the militiamen out of the city.

Al-Jazeera covered the developments in Najaf on Saturday, broadcasting live images of Sadr's militia members toting guns. It also broadcast a video that appeared to show an American man being beheaded but turned out to be a hoax.

Iraqi government leaders have complained repeatedly about al-Jazeera's practice of broadcasting videos showing kidnapped foreigners, alleging that the Qatar-based channel has ties to the captors.

On Saturday, the government shut down al-Jazeera's Baghdad offices. Allawi said an independent committee had been reviewing al-Jazeera's coverage of Iraq for a month and determined that it was contributing to the escalating violence.

Falah Naqib, Iraq's interior minister, accused the network of becoming "a venue for the terrorist, criminal factions."

"Instead of being a neutral means of reflecting truth, it opted to . . . spread fear among the peaceful Iraqi citizens," Naqib said at a news conference. "They give a bad picture on Iraq. They encouraged the criminals to increase their operations. We want to protect our people from Jazeera."

Jihad Ballout, a spokesman for the network, asked the government to reconsider the decision. "It badly affects the media and the Arab audience," Ballout said. "Nevertheless, we will try our best to cover the Iraqi field one way or another, because the Arab audience is interested in the situation in Iraq."

On the streets of Baghdad, there was mixed reaction to news of the government's actions against al-Jazeera.

Sabri Aleyesker, 47, who sells women's shoes in the Karada commercial district, said he watched al-Jazeera because it was not a mouthpiece for any one group or government. The government "closed it because they speak the truth," Aleyesker said.

But Saad Alfartousy, 37, said blocking al-Jazeera was "the best thing our government has done."

"They don't like Iraq, and they make the Iraqi people angry, and they push them to fight," he said. "Thank God, a thousand times, that they closed this channel."

Special correspondents Saad Sarhan in Najaf and Bassam Sebti, Luma Mousawi and Omar Fekeiki in Baghdad contributed to this report.