Hundreds of thousands of Shiites burned and trampled on US flags on Monday as they gathered in the Iraqi holy city of Najaf for an anti-American rally called by firebrand cleric Moqtada al-Sadr on the fourth anniversary of the fall of Saddam Hussein.
Large crowds of men, women and children holding Iraqi flags and anti-US banners massed in Najaf and the nearby twin city of Kufa to protest against what they said was an American occupation of Iraq.
The rally is seen as a show of strength for the cleric who has not been seen for more than two months, since the launch of a security crackdown in Baghdad aimed largely at reining in his militiamen accused of killing Sunni Arabs.
The US military has said he is in Iran but his aides deny the claims.
In the capital Baghdad, where four years ago on Monday a giant bronze statue of Saddam was torn down, dramatically symbolising the fall of his regime, security was tight.
A 24-hour vehicle curfew was in place and all Baghdad's key roads and bridges were deserted as people remained indoor for fear of attacks.
Jubilant Baghdadis who welcomed the invading US troops on April 9, 2003, now blame the rampant bloodshed and chaos on what even some of the country's most senior leaders brand an unwanted US-led "occupation."
The Shiite demonstrators are marching from Kufa to Najaf's central Sadrain Square where top aides of Sadr - who is regarded by the Americans as the most dangerous threat to stability in Iraq - are expected to address the crowds.
Hundreds of banners saying "Down with Bush, Down with America" could be seen in the crowd as Iraqi police and army soldiers guarded key checkpoints in and around Najaf and Kufa.
Many in the crowds were seen burning US flags and some were trampling on and striking US and Israeli flags painted on the ground with their shoes, an act considered one of the worst insults in Arab culture.
Some Sunni religious groups were also seen participating in the rally.
It was not known whether Sadr himself would address the crowds.
The cleric, who launched two bloody rebellions against US forces in 2004, is known for his anti-US stance and has emerged as a powerful force in the present Shiite-led Iraqi government.
His political bloc has 32 lawmakers in the 275-member parliament and six cabinet ministers in Prime Minister Nuri al-Maliki's embattled government.
On Sunday, he reiterated his call to unite against the Americans and end fighting between his militiamen and security forces in the central city of Diwaniyah.
"He appeals to the Iraqi army and the Mahdi militia not to fall into America's trap by fighting in Diwaniyah," said a statement stamped and issued by the cleric's Najaf office on his behalf.
US and Iraqi soldiers have been clashing with his militiamen in Diwaniyah since Friday.
Calling for unity against US troops, Sadr urged local forces not to support the "occupier because it is your enemy."
"Iraq has had enough bloodshed. The occupation forces led by the biggest evil, America, is working to sow dissent either directly or through its agents."
On April 9, 2003, US Marines pulled down the giant statue of Saddam by a rope around the neck, in a premonition of his hanging in December for crimes against humanity.
But gone are the euphoric cheers of "Good, Good, Bush" praising US President George W. Bush for ousting the regime. Angry chants of "Down with Bush" are a frequent background to brutal Shiite and Sunni sectarian strife.
About 80,000 US and Iraqi troops are now patrolling the capital's streets where although the daily execution-style killings are reported to be falling, high-profile car bombings remain a headache for security forces.
Since the invasion of March 20, 2003, tens of thousands of Iraqis have died in insurgent attacks and sectarian violence.
The four years have also been brutal for the US forces in Iraq.
On Monday, the military reported the deaths of six more soldiers in a series of attacks, taking its toll for the month alone to 27 and 3,275 since the invasion, according to Pentagon figures.