BAGHDAD, April 9 — Tens of thousands of protesters loyal to Moktada al-Sadr, the Shiite cleric, took to the streets of the holy city of Najaf on Monday in an extraordinarily disciplined rally to demand an end to the American military presence in Iraq, burning American flags and chanting “Death to America!”

Residents said that the angry, boisterous demonstration was the largest in Najaf, the heart of Shiite religious power, since the American-led invasion in 2003. It took place on the fourth anniversary of the fall of Baghdad, and it was an obvious effort by Mr. Sadr to show the extent of his influence here in Iraq, even though he did not appear at the rally. Mr. Sadr went underground after the American military began a new security push in Baghdad on Feb. 14, and his whereabouts are unknown.

Mr. Sadr used the protest to try to reassert his image as a nationalist rebel who appeals to both anti-American Shiites and Sunni Arabs. He established that reputation in 2004, when he publicly supported Sunni insurgents in Falluja who were battling United States marines, and quickly gained popularity among Sunnis across Iraq and the region. But his nationalist credentials have been tarnished in the last year, as Sunni Arabs have accused Mr. Sadr’s militia, the Mahdi Army, of torturing and killing Sunnis.

Iraqi policemen and soldiers lined the path taken by the protesters, and there were no reports of violence during the day. The American military handed security oversight of the city and province of Najaf to the Iraqi government in December, and the calm atmosphere showed that the Iraqi security forces could maintain control, keeping suicide bombers away from an obvious target. In March, when millions of Shiite pilgrims flocked to the holy cities of the south, Iraqi security forces in provinces adjoining Najaf failed to stop bombers from killing scores of them.

Vehicles were not allowed near Monday’s march, and Baghdad had a daylong ban on traffic to prevent outbreaks of violence.

During the protest in Najaf, Sadr followers draped themselves in Iraqi flags and waved them to symbolize national unity, and a small number of conservative Sunni Arabs took part in the march.

“We have 30 people who came,” said Ayad Abdul Wahab, an agriculture professor in Basra and an official in the Iraqi Islamic Party, a leading fundamentalist Sunni Arab group. “We support Moktada in this demonstration, and we stress our rejection of foreign occupation.”

He and his friends together carried a 30-foot-long Iraqi flag.

In the four years of war, the only other person who has been able to call for protests of this scale has been Grand Ayatollah Ali al-Sistani, Iraq’s most powerful Shiite cleric, who, like Mr. Sadr, has a home in Najaf.

The protest was in some ways another challenge to the Shiite clerical hierarchy, showing that in the new Iraq, a violent young upstart like Mr. Sadr can command the masses right in the backyard of venerable clerics like Ayatollah Sistani. Mr. Sadr has increasingly tapped into a powerful desire among Shiites to stand up forcefully to both the American presence and militant Sunnis, and to ignore calls for moderation from older clerics.

Lt. Col. Christopher Garver, an American military spokesman in Baghdad, said that American officers had helped officials in Najaf plan security for the event, but that the Iraqis had taken the lead.

Colonel Garver and other American officials tried to put the best possible light on the event, despite the fiery words. “We say that we’re here to support democracy,” he said. “We say that free speech and freedom of assembly are part of that. While we don’t necessarily agree with the message, we agree with their right to say it.”

The protest unfolded as heavy fighting continued in parts of Diwaniya, a southern city where American and Iraqi forces have been battling cells of the Mahdi Army since Friday. Mr. Sadr issued a statement on Sunday calling for the Mahdi militiamen and the Iraqi forces there to stop fighting each other, but those words went unheeded. Gun battles broke out on Monday, and an American officer said at a news conference that at least one American soldier had been killed and one wounded in four days of clashes.

That fighting and the protest in Najaf, as well as Mr. Sadr’s mysterious absence, raise questions about how much control he actually maintains over his militia. Mr. Sadr is obviously still able to order huge numbers of people into the streets, but there has been talk that branches of his militia have split off and now operate independently. In Baghdad, some Mahdi Army cells have refrained in the last two months from attacking Americans and carrying out killings of Sunni Arabs, supposedly on orders from Mr. Sadr, but bodies of Sunnis have begun reappearing in some neighborhoods in recent weeks.

The protest in Najaf was made up mostly of young men, many of whom drove down from the sprawling Sadr City section of Baghdad, some 100 miles north, the previous night. They gathered Monday morning in the town of Kufa, where Mr. Sadr has his main mosque, and walked a few miles to Sadrain Square in Najaf. Protesters stomped on American flags and burned them. “No, no America; leave, leave occupier,” they chanted. At Sadrain Square, the protesters listened to a statement read over loudspeakers that was attributed to Mr. Sadr.

“Oh Iraqi people, you are aware, as 48 months have passed, that we live in a state of oppression, unjust repression and occupation,” the statement read. “Forty-eight hard months — that make four years — in which we have gotten nothing but more killing, destruction and degradation. Tens of people are being killed every day. Tens are disabled every day.”

Mr. Sadr added: “America made efforts to stoke sectarian strife, and here I would like to tell you, the sons of the two rivers, that you have proved your ability to surpass difficulties and sacrifice yourselves, despite the conspiracies of the evil powers against you.”

An Interior Ministry employee in a flowing tan robe, Haider Abdul Rahim Mustafa, 23, said that he had come from Basra “to demand the withdrawal of the occupier.”

“The occupier supported Saddam and helped him to become stronger, then removed him because his cards were burned,” he said, using an Arabic expression to note that Saddam Hussein was no longer useful to the United States. “The fall of Saddam means nothing to us as long as the alternative is the American occupation.”

Estimates of the crowd’s size varied wildly. A police commander in Najaf, Brig. Gen. Abdul Karim al-Mayahi, said there were at least half a million people. Colonel Garver said that military reports had estimates of 5,000 to 7,000. Residents and other Iraqi officials said there were tens of thousands, and television images of the rally seemed to support their estimates.

The colonel declined to give any information on the whereabouts of Mr. Sadr, though American military officials said weeks ago that they believed he is in Iran. Mr. Sadr’s aides declined to say where he is, but previously they have said he remained in Iraq.

BAGHDAD, April 9 — Tens of thousands of protesters loyal to Moktada al-Sadr, the Shiite cleric, took to the streets of the holy city of Najaf on Monday in an extraordinarily disciplined rally to demand an end to the American military presence in Iraq, burning American flags and chanting “Death to America!”

Residents said that the angry, boisterous demonstration was the largest in Najaf, the heart of Shiite religious power, since the American-led invasion in 2003. It took place on the fourth anniversary of the fall of Baghdad, and it was an obvious effort by Mr. Sadr to show the extent of his influence here in Iraq, even though he did not appear at the rally. Mr. Sadr went underground after the American military began a new security push in Baghdad on Feb. 14, and his whereabouts are unknown.

Mr. Sadr used the protest to try to reassert his image as a nationalist rebel who appeals to both anti-American Shiites and Sunni Arabs. He established that reputation in 2004, when he publicly supported Sunni insurgents in Falluja who were battling United States marines, and quickly gained popularity among Sunnis across Iraq and the region. But his nationalist credentials have been tarnished in the last year, as Sunni Arabs have accused Mr. Sadr’s militia, the Mahdi Army, of torturing and killing Sunnis.

Iraqi policemen and soldiers lined the path taken by the protesters, and there were no reports of violence during the day. The American military handed security oversight of the city and province of Najaf to the Iraqi government in December, and the calm atmosphere showed that the Iraqi security forces could maintain control, keeping suicide bombers away from an obvious target. In March, when millions of Shiite pilgrims flocked to the holy cities of the south, Iraqi security forces in provinces adjoining Najaf failed to stop bombers from killing scores of them.

Vehicles were not allowed near Monday’s march, and Baghdad had a daylong ban on traffic to prevent outbreaks of violence.

During the protest in Najaf, Sadr followers draped themselves in Iraqi flags and waved them to symbolize national unity, and a small number of conservative Sunni Arabs took part in the march.

“We have 30 people who came,” said Ayad Abdul Wahab, an agriculture professor in Basra and an official in the Iraqi Islamic Party, a leading fundamentalist Sunni Arab group. “We support Moktada in this demonstration, and we stress our rejection of foreign occupation.”

He and his friends together carried a 30-foot-long Iraqi flag.

In the four years of war, the only other person who has been able to call for protests of this scale has been Grand Ayatollah Ali al-Sistani, Iraq’s most powerful Shiite cleric, who, like Mr. Sadr, has a home in Najaf.

The protest was in some ways another challenge to the Shiite clerical hierarchy, showing that in the new Iraq, a violent young upstart like Mr. Sadr can command the masses right in the backyard of venerable clerics like Ayatollah Sistani. Mr. Sadr has increasingly tapped into a powerful desire among Shiites to stand up forcefully to both the American presence and militant Sunnis, and to ignore calls for moderation from older clerics.

Lt. Col. Christopher Garver, an American military spokesman in Baghdad, said that American officers had helped officials in Najaf plan security for the event, but that the Iraqis had taken the lead.

Colonel Garver and other American officials tried to put the best possible light on the event, despite the fiery words. “We say that we’re here to support democracy,” he said. “We say that free speech and freedom of assembly are part of that. While we don’t necessarily agree with the message, we agree with their right to say it.”

The protest unfolded as heavy fighting continued in parts of Diwaniya, a southern city where American and Iraqi forces have been battling cells of the Mahdi Army since Friday. Mr. Sadr issued a statement on Sunday calling for the Mahdi militiamen and the Iraqi forces there to stop fighting each other, but those words went unheeded. Gun battles broke out on Monday, and an American officer said at a news conference that at least one American soldier had been killed and one wounded in four days of clashes.

That fighting and the protest in Najaf, as well as Mr. Sadr’s mysterious absence, raise questions about how much control he actually maintains over his militia. Mr. Sadr is obviously still able to order huge numbers of people into the streets, but there has been talk that branches of his militia have split off and now operate independently. In Baghdad, some Mahdi Army cells have refrained in the last two months from attacking Americans and carrying out killings of Sunni Arabs, supposedly on orders from Mr. Sadr, but bodies of Sunnis have begun reappearing in some neighborhoods in recent weeks.

The protest in Najaf was made up mostly of young men, many of whom drove down from the sprawling Sadr City section of Baghdad, some 100 miles north, the previous night. They gathered Monday morning in the town of Kufa, where Mr. Sadr has his main mosque, and walked a few miles to Sadrain Square in Najaf. Protesters stomped on American flags and burned them. “No, no America; leave, leave occupier,” they chanted. At Sadrain Square, the protesters listened to a statement read over loudspeakers that was attributed to Mr. Sadr.

“Oh Iraqi people, you are aware, as 48 months have passed, that we live in a state of oppression, unjust repression and occupation,” the statement read. “Forty-eight hard months — that make four years — in which we have gotten nothing but more killing, destruction and degradation. Tens of people are being killed every day. Tens are disabled every day.”

Mr. Sadr added: “America made efforts to stoke sectarian strife, and here I would like to tell you, the sons of the two rivers, that you have proved your ability to surpass difficulties and sacrifice yourselves, despite the conspiracies of the evil powers against you.”

An Interior Ministry employee in a flowing tan robe, Haider Abdul Rahim Mustafa, 23, said that he had come from Basra “to demand the withdrawal of the occupier.”

“The occupier supported Saddam and helped him to become stronger, then removed him because his cards were burned,” he said, using an Arabic expression to note that Saddam Hussein was no longer useful to the United States. “The fall of Saddam means nothing to us as long as the alternative is the American occupation.”

Estimates of the crowd’s size varied wildly. A police commander in Najaf, Brig. Gen. Abdul Karim al-Mayahi, said there were at least half a million people. Colonel Garver said that military reports had estimates of 5,000 to 7,000. Residents and other Iraqi officials said there were tens of thousands, and television images of the rally seemed to support their estimates.

The colonel declined to give any information on the whereabouts of Mr. Sadr, though American military officials said weeks ago that they believed he is in Iran. Mr. Sadr’s aides declined to say where he is, but previously they have said he remained in Iraq.

In Diwaniya, hospital officials said their wards were overwhelmed by casualties. There was a shortage of food and oxygen, and ambulances were being blocked from the scene of combat, said Dr. Hamid Jaati, the city’s health director. The main hospital received 13 dead Iraqis and 41 injured ones over the weekend, he added.

The fighting started Friday after the provincial council and governor called for the Iraqi Army and American forces to take on the Sadr militiamen. The governor and 28 of 40 council members belong to a powerful Shiite party called the Supreme Council for the Islamic Revolution in Iraq, which is the main rival to the Sadr organization. Sadr officials have accused the party of using the military to carry out a political grudge, but the governor, Khalil Jalil Hamza, denied that on Monday.

In Diyala Province, northeast of Baghdad, a suicide car bomb killed three civilians and wounded four others on Sunday night, police officials said Monday. Also in Diyala, a local politician was fatally shot on Monday in Hibhib, and three bodies were found in Khalis.

In Diwaniya, hospital officials said their wards were overwhelmed by casualties. There was a shortage of food and oxygen, and ambulances were being blocked from the scene of combat, said Dr. Hamid Jaati, the city’s health director. The main hospital received 13 dead Iraqis and 41 injured ones over the weekend, he added.

The fighting started Friday after the provincial council and governor called for the Iraqi Army and American forces to take on the Sadr militiamen. The governor and 28 of 40 council members belong to a powerful Shiite party called the Supreme Council for the Islamic Revolution in Iraq, which is the main rival to the Sadr organization. Sadr officials have accused the party of using the military to carry out a political grudge, but the governor, Khalil Jalil Hamza, denied that on Monday.

In Diyala Province, northeast of Baghdad, a suicide car bomb killed three civilians and wounded four others on Sunday night, police officials said Monday. Also in Diyala, a local politician was fatally shot on Monday in Hibhib, and three bodies were found in Khalis.