Radical cleric Muqtada al-Sadr (search) told his militiamen to give up control of the holy Imam Ali Shrine Thursday, hours after Iraq’s prime minister issued a "final call" for his fighting force to disarm.

Meanwhile, bomb blasts and gunfire resounded through the streets of Najaf, (search) and U.S. warplanes bombarded militant positions. At night, at least 30 explosions shook the Old City as an American aircraft bombed targets east of the revered shrine.

The fighting with al-Sadr’s forces wasn’t limited to Najaf. U.S. troops also battled his militia in a Baghdad slum, where militants said five fighters and five civilians were killed. Also, late Thursday, a U.S. warplane bombed targets in the flashpoint Sunni city of Fallujah (search), 40 miles west of Baghdad.

Amid calls of “God is Great” and passages from the Quran pumping through mosque loudspeakers, Fallujah’s guerrillas launched a barrage of mortars toward a U.S. base. American forces routinely bomb targets there, believing the city is home to strongholds of Sunnis who have attacked coalition troops, Iraqi forces and civilians.

Elsewhere, insurgents attacked oil facilities in the north and south, fired mortars at U.S. Embassy offices in the capital, injuring one American, and reportedly threatened to kill two hostages, a Turkish worker and a U.S. journalist.

In a speech, interim Prime Minister Iyad Allawi (search) had warned the radical cleric to disarm his forces and withdraw from the shrine after his government threatened to send a massive Iraqi force to root them out.

Defying that ultimatum, al-Sadr sent a telephone text message vowing to seek "martyrdom or victory," and his jubilant followers inside the shrine danced and chanted.

Later in the day, Aws al-Khafaji, a top aide to the cleric, told the pan-Arab Al-Jazeera television station that al-Sadr asked his armed supporters to cede the Imam Ali Shrine compound to the office of Grand Ayatollah Ali al-Sistani (search), the top Shiite cleric in Iraq.

"I call on the religious authority again to receive the shrine so that it won't be taken by the hands of the enemy and of treason. I have offered it to you before and you have refused before the (latest) incidents," read a letter al-Sadr reportedly sent to his followers, as shown on Al-Arabiya television. The seal of al-Sadr's office was on the letter, but his signature was not, according to the station.

But the cleric refused to dissolve his fighting force. The letter contended the militia belonged to Imam Mahdi (search), the Shiite messiah.

"Let everyone know that this army is the Imam Mahdi's base, and I have no right to ever disband it," the letter said.

Al-Sadr had said in recent days he wanted to make sure the shrine was in the custody of religious authorities, though it was unclear if the government would agree to that.

The violence in the holy city between the insurgents and a combined U.S.-Iraqi force has angered many in Iraq's Shiite majority and proven a major challenge to Allawi's fledgling interim government as it tries to build credibility and prove it is not a U.S. puppet.

Any raid to oust militants from the Imam Ali shrine -- especially one that damaged the holy site -- could spark a far larger Shiite uprising. Government accusations that militants have mined the shrine compound and reports that women and children were among those inside could further complicate a raid.

In the impoverished Baghdad neighborhood of Sadr City -- named for the cleric's late father -- U.S. tanks moved throughout the streets and helicopter gunships shot at al-Sadr militants from the skies. The militants claimed five fighters and five civilians were killed.

There was no certainty that the latest offer from al-Sadr to withdraw would be implemented, as both sides appeared to be engaged in brinkmanship.

Thursday's violence came a day after al-Sadr had accepted an Iraqi delegation's peace plan for Najaf, demanding he disarm his militia, leave the shrine and turn to politics in exchange for amnesty. But he continued to attach conditions the government rejected, and fighting persisted.

Reiterating his government's refusal to negotiate with the armed militants, Allawi had called on al-Sadr to personally accept the government's demands to end the Najaf fighting -- not through aides or letters as he has been communicating so far.

"When we hear from him and that he is committed to execute these conditions we will ... give him and his group protection," the prime minister said in a Baghdad news conference.

In Washington, the Bush administration said al-Sadr needed to match words with deeds. "We have seen many, many times al-Sadr assume or say he is going to accept certain terms and then it turns out not to be the case," said National Security Adviser Condoleezza Rice.

Other Muslim countries, including Shiite Iran, have appealed to the Iraqi government to seek a peaceful solution, and the Arab League chief on Thursday called for an immediate end to military operations in Najaf and said Iraqi civilians must be spared.

Secretary-General Amr Moussa received news of artillery "shelling and renewed clashes (in Najaf) with great uneasiness," Arab League spokesman Hossam Zaki said in a statement faxed to The Associated Press.

An al-Sadr representative in Baghdad, Abdel-Hadi al-Darraji, warned that fighting in Najaf could "ignite a revolution all over Iraq."

"We welcome any initiative to stop the bloodbath in Najaf," he told Al-Arabiya television. "Otherwise the battle will move to Baghdad, Amarah, Basra and anywhere in Iraq."

Hoping to undermine efforts to stabilize and rebuild after the ousting of Saddam Hussein (search), militants have frequently attacked Iraq's essential oil industry. Al-Sadr fighters on Thursday broke into the headquarters of Iraq's South Oil Co. near the southern city of Basra and set the company's warehouses and offices on fire, witnesses said.

A separate attack near the northern city of Kirkuk killed an Iraqi security officer working for the state-run Northern Oil Co. and injured two others, police said.

The Associated Press contributed to this report.