Hundreds of thousands of Shiite Muslim (more news | Web) pilgrims marched into the Iraqi holy city of Karbala Tuesday, taking part in religious rituals banned by Saddam Hussein (more news | Web) for the past quarter-century.

Iraqi Shiite leaders were flexing their political muscles for the first time in decades, but there was more than anti-Saddam sentiment surrounding the pilgrimage. Many Shiites want America out of Iraq too.

Meanwhile, one of Saddam Hussein's most feared lieutenants landed in U.S. hands. Muhammad Hamza al-Zubaydi (more news | Web), otherwise known as Saddam's "Shiite thug" for his role in the suppression of the Shiite uprising of 1991, is a former prime minister and was No. 18 -- the "queen of spades" -- in the U.S. military's 55-deck of Iraq's most wanted.

Up to 2 million Shiites from Iraq, Iran and other Middle Eastern countries worshipped at Karbala's holy shrine Tuesday, chanting, dancing, even cutting their bodies in a frenzied religious ritual that had been banned by the secular-minded, Sunni-dominated Baath Party that spawned Saddam.

Karbala (more news | Web) the site of the 7th-century martyrdom of Imam Hussein, a grandson of the Prophet Muhammad and one of Shia Islam's most revered saints. The annual pilgrimage culminates Thursday.

Pilgrims also streamed toward the nearby city of Najaf, home to the tomb of Imam Ali, Hussein's father and the Prophet's son-in-law, and to Shiites, the holiest city in Islam after Mecca and Medina.

The event was peaceful for the most part, although the U.S. military said Tuesday that police in Karbala arrested six men who had been planning to blow up two of the city's mosques.

Five of the detainees claimed to be members of Saddam's Baath Party, and one said he belonged to Al Qaeda, said Capt. Jimmie Cummings, spokesman for the Army's 82nd Airborne Division. The men were arrested Monday and were handed over to the 101st Airborne Division in Karbala.

Since Saddam's fall, Shiites have been setting up local administrations to re-establish order, and religious leaders have emerged as key sources of political power, especially in southern Iraq.

"It is a symbol of Shiite unity and their rejection of oppression and injustice," said Hamid al-Bayati, representative of the Iran-based Supreme Council for the Islamic Revolution in Iraq.

"It's an expression of their yearning for freedom," he said from his London office.

At least one leading Shiite has called for the Karbala gathering to be used as a protest against U.S. domination of Iraq. Some pilgrims chanted anti-American slogans.

"Yes, yes to Islam, no to America, no to Israel, no to colonialism and no to occupation," chanted men marching in Karbala behind a portrait of Mohammed Sadeq al-Sadr, an Iraqi Shiite cleric killed with his two sons in 1999.

But Brig. Gen. Vincent Brooks, speaking at a U.S. Central Command briefing in Qatar on Tuesday, noted that pilgrims were "participating in something that would not have been possible before. And thus far it has occurred without any significant incidents."

Coalition forces want to form an interim government and help the Iraqis choose their leaders. But many Shiites are angered by what they see as U.S. intervention.

"It is a message to the Americans: If you interfere, we shall fight you. These people are ready to be killed for freedom, because we want a Shiite leadership," a pilgrim said.

The pilgrims included men and women of all ages - the men clad mostly white robes and headbands, the women cloaked head-to-toe in traditional black dress.

Coalition troops tried to keep a low profile during the pilgrimage as they stacked food and water along roads leading to Karbala. No American troops were actually in the city.

Members of the Free Iraqi Forces, the military wing of the U.S.-backed Iraqi National Congress, were seen checking cars. Some of them wore black headbands, a symbol of mourning, traditional for Shiites during the 40-day period after the anniversary of the death of Imam Hussein.

Two groups of 100 men slashed their heads with long sharp swords in a self-mutilation ritual Tuesday and waved the blades at the shrine, screaming with joy.

"People used to be detained if they were seen beating their chests near or inside the shrine," said Ouza Qateh, 42, who walked from Basra to Nasiriyah and then drove to Karbala. "They were practicing terrorism and fear against Shiites."

Packs of men circled the city's main shrines, creating a vortex of humanity. Some worshippers carried photos of famous Shiite clerics.

Inside the shrine, groups of the faithful beat their chests and screamed: "You dirty Saddam, where are you so that we can fight you?"

Ahmed Abdel-Whaed, 28, of Baghdad, said, "He who dared to march ... used to disappear." Abdel-Whaed had just returned to Iraq from Jordan, where he fled two years ago out of fear of persecution.

Water trucks were brought in to help the crowd - which already may have surpassed 1 million people - weather Tuesday's 90-degree heat and blazing sun.

A portrait of Saddam that used to hang on the main Imam Hussein shrine was noticeably absent.

The roads in the area were choked with pilgrims, some of them limping from long journeys. Two men crawled on their stomachs into one shrine; months back, they had vowed to crawl into Karbala if the Americans ousted Saddam.

"We were prohibited from visiting these shrines for a long time by the Baath Party and their agents," Abed Ali Ghilan told APTN in Karbala. "This year we thank God for ridding us of the dictator Saddam Hussein and for letting us visit these shrines."

Saddam's regime permitted the annual pilgrimages, but prohibited people from coming on foot or engaging in the ritual slashings, and monitored the participants as well as holy sites in Najaf and Karbala.

But rifts have already erupted among the Shiites.

Abdul Majid al-Khoei, an exiled cleric who had opposed Saddam's rule but came back to Iraq to help reconstruction efforts, was hacked to death April 10 at the Ali Mosque in Najaf along with a pro-Saddam cleric with whom he appeared as a gesture of reconciliation.

Al-Zubaydi, the former vice president who was captured Monday, was the highest-ranking figure on the U.S. military's most-wanted list to be caught so far.

Tens of thousands of people died in the revolt following the 1991 Gulf War, which al-Zubaydi helped suppress. Iraqi opposition groups have also accused al-Zubaydi of the 1999 assassination of Shiite leader Mohammed Sadeq al-Sadr.

Al-Zubaydi was considered one of the most brutal figures in the regime. A Shiite himself, he was once featured in an Iraqi videotape brutalizing Shiite dissidents.

"This is very significant - he is one of the most hated men in the former regime," said Haider Ahmad, a spokesman for the Iraqi National Congress, the umbrella exile group led by Ahmad Chalabi.

The Associated Press contributed to this report.