NAJAF, Iraq (AFP) -- Thousands of supporters of Iraq's radical Shiite cleric Moqtada al-Sadr on Sunday prepared to stage a massive anti-U.S. rally on Monday's fourth anniversary of the fall of Baghdad, police said.

Police Colonel Ali Jiraou confirmed that thousands of Sadr movement members were in Najaf south of Baghdad and that security measures were being made to protect them.

Hundreds of Iraqi flags were raised over government buildings in Najaf and in public squares, according to an AFP journalist.

The demonstration is scheduled to begin on Monday outside Sadr's mosque in Kufa and proceed into the twin Shiite shrine city of Najaf, a member of Sadr's office in Najaf told AFP on condition of anonymity.

He said thousands of Sadr sympathizers were traveling to Najaf to join the demonstration against the U.S.-led foreign "occupation" of Iraq.

"It will be an Iraqi demonstration in the name of all Iraqis. We will raise the Iraqi flag and also banners demanding that the occupation leave," he said. Oudha Mohammed, a representative of Sadr in the southern Shiite city of Basra, said thousands of residents had left for Najaf following Sadr's call to demonstrate against the "occupation."

A spokesman for Najaf governorate, Ahmed Duaibil, confirmed that a joint committee of Sadr supporters and provincial administrators would be set up to ensure the safety of protesters.

On March 30, Sheikh Abdul Hadi al-Muhamadawi, speaking on behalf of Sadr in Kufa, urged Iraqis to protest on April 9, the fourth anniversary of the fall of Baghdad and the overthrow of former president Saddam Hussein.

Sadr, whose Mahdi Army militia is branded the most dangerous element in Iraq by the Pentagon and whom the Americans believe has fled to Iran, has always demanded that U.S. troops leave the country.