A prominent Shiite Muslim cleric who recently returned to Iraq from exile in Britain to preach reconciliation and acceptance of the U.S. invasion was killed by a mob today inside one of Islam's holiest shrines, along with a fellow cleric who had served in deposed president Saddam Hussein's government.

Abdul Majid Khoei, son of one of Shiite Islam's most revered leaders, and Haider Kadar, an official of Hussein's Ministry of Religion, had come to the Imam Ali Mosque to conduct a ceremony of reconciliation. According to eyewitnesses and news reports, they were set upon there by assailants with knives.

The killings underlined the continuing instability and danger of widespread score-settling in post-Hussein Iraq, and the ambivalent feelings of many members of the country's Shiite population about the war. While many have celebrated the overthrow of Hussein, who is from the country's Sunni Muslim minority, they remain suspicious of the motives of the United States and its Iraqi allies.

According to an official at the Al-Khoei Foundation that Khoei ran in London, an eyewitness reported that a group of men first attacked Kadar, then Khoei when he attempted to protect his fellow cleric. Rescuers carried the wounded Khoei to a nearby shop, but assailants followed and killed him there, according to this account.

There was confusion over the identity and motives of the assailants. The London official, Sayyed Nadeem Kazmi, said the mob consisted of Hussein opponents who objected to Kadar's presence at the mosque, but might have been incited by agents of Hussein's government.

But Laith Kubba, an Iraqi opposition leader and former director of the foundation, said he believed the killings had nothing to do with Hussein's agents. Rather, he said, they reflected internal rivalries in Najaf and the opposition of those who mistrusted Khoei's attempts to preach reconciliation.

"It's a terrible loss to the cause of peace in Iraq," said Kubba. Khoei "wanted to make sure that chaos and revenge killings would not take place, and he went out of his way to reassure policemen that they would not be a target. He upset some of the locals. It's an indication of how awful things are right now."

Khoei, 41, was the son of Grand Ayatollah Abolqassem Khoei, the supreme Shiite spiritual leader at the time of the 1991 Shiite uprising after the Persian Gulf War. The revolt was crushed by Hussein's troops after the U.S. government, which had encouraged the uprising, declined to use its own troops to support it. Hussein later forced the ayatollah, then 95, to submit to a televised meeting that was widely seen as a gesture of humiliation. He died under house arrest a year later.

His son fled Iraq at that time, taking up residence in London, where he founded a charitable group. He returned to southern Iraq two weeks ago, and was helping U.S. and British forces establish calm in cities such as Najaf, which has long been the seat of ayatollahs and an important center of Islamic studies. The mosque where the killings took place is the tomb of Ali, the Prophet Muhammad's son-in-law.

Khoei arrived in Najaf a week ago, and was attempting to help local clerics negotiate a deal under which Hussein loyalists who had taken refuge in the mosque would leave it in return for safe passage out of the city, according to news reports. He generally was accompanied by U.S. soldiers as he moved around the tense city, witnesses said. But he did not take a military escort inside the mosque today. It was not clear whether his cooperation with coalition forces was a factor in his killing.

The U.S. military flew in journalists aboard two helicopters to witness the reconciliation ceremony, the Associated Press reported. But they arrived after the killings.

Witnesses agreed that Khoei and Kader entered the mosque together with four other men. Members of Kadar's family traditionally have been keyholders to the shrine.

The Associated Press cited a witness who said the men were first assailed verbally by a faction loyal to a mullah who was assassinated with his two sons in Najaf in 1999, Mohammad Sadiq Sadr. People in Najaf believe those killings were done by Hussein's government.

Another witness, Maad Fayyad, a local writer and journalist, told al-Jazeera television that he was with Khoei and four others in an office inside the mosque when the trouble started. A mob came with guns, knives and swords asking to avenge the death of Sadr.

They demanded that Kadar be handed over for execution. "They were all revved up for a massacre," Fayyad said.

Apparently feeling threatened, Khoei pulled a gun and fired one or two shots, according to the news reports. There were conflicting accounts over whether he fired the bullets into the air or the crowd. Both men were then rushed by the crowd and hacked with swords and knives, the witnesses said.

Kazmi disputed the claim that Khoei fired his weapon. "He carried a gun with him for protection, but he never used it," said Kazmi.

Long oppressed by the Baath Party government, the Shiites have been reluctant to embrace occupying U.S. forces.

One prominent Shiite group, the Iranian-backed Supreme Council of the Islamic Revolution in Iraq, has issued a warning that U.S.-led forces should leave as soon as they finish toppling Hussein's government. "Iraqis will resist if they seek to occupy or colonize our country," declared the group's leader, Ayatollah Mohammed Bakir Hakim, speaking in Tehran.

Khoei had told followers he understood why they were reluctant to cooperate with the Americans, but he urged them to put their suspicions aside. In recent days, he had said he believed he was making progress in healing wounds from decades of brutal rule, Kazmi said.

British Prime Minister Tony Blair, who had met with Khoei several times, said he was appalled and saddened at the cleric's death.

Boustany reported from Washington. Researcher Robert Thomason contributed to this report.

Abdul Majid Khoei, a leading Islamic cleric killed outside a mosque in Najaf, Iraq, met with British Prime Minister Tony Blair in London in October 2001.