An angry crowd confronted Iraq's former Prime Minister Ayad Allawi at a Shiite shrine south of Baghdad on Sunday, forcing him to flee in a hail of stones and shoes. Allawi called the attack an assassination attempt.

In Baghdad, one of the five judges in the trial of Saddam Hussein stepped down because one of the co-defendants may have been involved in the execution of his brother, a court official said Sunday. Another official said police had uncovered a plot to fire rockets at the courtroom when the trial convenes Monday for a third session.

The confrontation in Najaf began when about a dozen men, some armed with clubs, tried to block Allawi from entering the Imam Ali mosque, one of the holiest Shiite shrines in Iraq. Allawi's bodyguards fired shots in the air to disperse the crowd.

Once Allawi and his entourage were inside, the crowd grew to about 60 and as the group left, they were showered with stones and shoes — a sign of contempt in Iraqi culture. Allawi and his security force knocked over barricades as they scampered to their vehicles and sped away.

Allawi later said the group was armed with pistols, knives and swords and at least seven shots were fired from the crowd.

"They were planning to kill the whole delegation, or at least me," Allawi told reporters.

Foreign Minister Hoshyar Zebari told a cable news network that it was unclear whether the incident was an assassination attempt "or just a disruption by the angry crowd who might not agree with Dr. Allawi's policy."

Allawi, a secular Shiite, is a candidate for parliament in the Dec. 15 election, running at the head of a broad-based ticket that includes several prominent Sunni Arabs. When he was prime minister, U.S. and Iraqi troops seized control of Najaf from the firebrand cleric Muqtada al-Sadr. Many Shiites have not forgiven Allawi for his role in the assault, and many in the crowd of attackers were believed to be al-Sadr followers.

Allawi, a former member of Saddam's Baath party, also earned the contempt of many Shiites for recruiting veterans of the ousted regime's security services to bolster Iraq's military and intelligence resources in the fight against the Sunni-led insurgents.

Tensions are running high across Iraq in advance of the Dec. 15 election, during which Iraqis will choose a parliament to serve for a full four-year term. A coalition of Shiite religious parties is expected to win the largest share of the 275 seats.

In other violence Sunday, gunmen killed a Shiite parliamentary candidate and an Iraqi police commander in separate attacks. A bomb also detonated as a police patrol passed through central Baghdad, killing three civilians.

Amid the tension, the Iraqi High Tribunal convenes Monday for a third session of the trial of Saddam and seven co-defendants, accused in the 1982 killing of more than 140 Shiites after an assassination attempt against the president in Dujail.

The defense has challenged the legitimacy of the court and is expected to ask for a recess to prepare its case.

A statement released Sunday by the office of Mouwaffak al-Rubaie, Iraq's national security adviser, said the 1920 Revolution Brigades, one of the country's best-known insurgent groups, planned to attack the building during the court session.

The statement said Iraqi intelligence uncovered the plot but gave no further details, including whether anyone had been arrested.

Since the trial opened, two defense lawyers have been assassinated and a third has fled the country.

A U.S. official close to the proceedings told reporters that the court Monday will begin hearing testimony from 10 witnesses, six of whom have agreed to have their identities revealed but insisted that they not be shown on television for security reasons.

Two others insisted on testifying behind a screen, and the others agreed to appear without any restrictions, the official said, speaking on condition of anonymity because of the sensitivity of the subject.

He said the defense had submitted three motions — challenging the legitimacy of the tribunal, arguing that Saddam's actions were protected by presidential immunity and asking for more time to prepare its case. It was unclear if the judges would rule on them Monday.

The official predicted the hearings would last three or four days before adjourning until after national parliamentary elections Dec. 15. Iraqi officials have said that holding the trial during the election would strain the country's security resources.

Each of the eight defendants will have at least one attorney in court Monday.

The five-member judicial panel hearing the case will include one new judge who replaced one who asked to be removed after learning that one of the defendants may have been linked to the execution of his brother, court official Raid Juhi said.

Names of both judges were not released because under security rules, the identities of all panel members are kept secret except for Chief Judge Rizgar Mohammed Amin.

In Jordan, former Attorney General Ramsey Clark told reporters he and other international lawyers will meet Saddam after the hearing Monday to set out a defense strategy.

"It will be our first real meeting where we'll have the chance to discuss the trial," Clark told AP Television News before flying to Baghdad on Sunday. "He's being held in total isolation, not seeing any member of his family, any friend, anybody he knew before."

The slow pace of the trial — which has included only two one-day sessions so far — has drawn criticism from Shiite politicians. Some Shiite figures have urged supporters to vote for the main Shiite ticket on Dec. 15 to prevent Saddam from escaping justice.

During the Nov. 28 session, Saddam lashed out at his treatment by American "occupiers and invaders" and lectured the chief judge about leadership.