BAGHDAD, Iraq -- An influential anti-U.S. Shiite cleric yesterday joined the campaign to get Sunni Arab Muslim leaders to help quell the sectarian violence now roiling Iraq, even as insurgents continued their attacks against government officials and U.S. troops.

Muqtada al-Sadr, who commands thousands of militia fighters in the capital's slums, sent a delegation to meet with Sunni leaders and appeal for an end to tensions.

At least 10 Shiite and Sunni clerics have been killed in recent weeks, prompting speculation that they were tit-for-tat killings. The head of the Sunni Association of Muslim Scholars last week blamed several of the Sunni killings on the Badr Brigades, a Shiite paramilitary force linked to the Supreme Council of the Islamic Revolution in Iraq, the nation's largest Shiite political movement.

Sadr, who had been in hiding since a high-profile clash with U.S.-led forces last August, told Al-Arabiya satellite television that he had returned to the political scene to try to reconcile Muslim factions.

"Iraqis need to stand side by side at this time," Sadr said, warning that extremists were provoking civil war.

Sadr's return to prominence could be seen as a challenge to U.S. authority in Iraq. He and his militants have made withdrawal of foreign forces a prerequisite for participation in the emerging political process.

A U.S. official who spoke on condition of anonymity indicated that Sadr's activism will be tolerated by Washington so long as he refrains from "crossing red lines," or violating the U.S.-backed government's goal of peaceful restoration of order and national reconciliation.

Sadr's gesture followed Saturday's vow by Sunni clerics, politicians and tribal leaders to unite to recover a measure of the political clout they enjoyed before their patron Saddam Hussein was ousted. Shiites and Kurds now hold the most powerful positions in the new government. The Sunni leaders said they would try to forge a common strategy for engagement with Shiites and Kurds in drafting a new constitution and in campaigning for the National Assembly to be elected in December.

Sunnis who belonged to Saddam's disbanded Baathist Party have been blamed for driving the insurgency that continues to frustrate reconstruction efforts and security more than two years after the U.S.-led invasion brought 150,000 foreign troops to Iraq. In less than four weeks since the new Iraqi government took power, more than 550 people have died in a wave of suicide attacks, drive-by shootings and roadside bombings.

Seven Iraqi battalions backed by U.S. forces launched an offensive in Baghdad yesterday in an effort to stanch the violence, The Associated Press reported. The U.S. military said the offensive in the west of the capital had been set in motion to root out insurgents, especially those who have conducted bloody assaults on the U.S.-run Abu Ghraib prison and the notoriously dangerous road from downtown to the airport.

Also, yesterday, insurgents assassinated Trade Ministry auditing chief Ali Moussa and his driver as they were making their way to his Baghdad office around 9 a.m., the latest in a barrage of killings of government officials.

The Justice Ministry confirmed that one of Saddam's jailed former lieutenants had been released from U.S. custody late last month so he could seek treatment for terminal cancer.

The decision to free Ghazi Hammud al-Obeidi, 65, the former Baathist leader for the city of Kut, was made by U.S. forces before the April 28 transfer of authority to Iraqi forces, said Abdulkarim Alinizy, deputy national security affairs minister. Alinizy suggested Obeidi could still be returned to Iraqi custody if a committee reviewing the decision so orders.