The faithful beat their chests and called for vengeance as they slowly followed a flatbed truck carrying a symbolic coffin for Ayatollah Mohammed Baqir al-Hakim, a moderate cleric and Saddam Hussein opponent. Authorities said they could only find al-Hakim's hand, watch, wedding band and pen.

"Our revenge will be severe on the killers," read one of the many banners carried by mourners.

Red and white roses were laid on the coffin and a large portrait of al-Hakim was placed in front of it.

The Iraqi police handling the investigation into Friday's bombing say they have arrested 19 men - many of them foreigners and all with admitted links to al-Qaeda - in connection with the blast. However, many Shiites blame the cleric's death on Saddam Hussein loyalists and the US-led coalition, which they say has failed to provide adequate security in the country since the dictator's fall.

"Saddam and Bush will not humiliate us," read another banner.

The procession began at the al-Kadhimiyah Shrine, one of Baghdad's most sacred Shiite sites, and was expected to grow as it weaved its way southward. The marchers were to stop at holy sites in Karbala before arriving at the blast site, Najaf's Imam Ali Shrine, for the funeral on Tuesday.

Police detained two Iraqis and two Saudis shortly after the Friday attack, and they provided information leading to the arrest of 15 other suspects, said a senior police official in Najaf, speaking on condition of anonymity.

Two Kuwaitis and six Palestinians with Jordanian passports were among the suspects, the official said. The remainder were Iraqis and Saudis, the official said, without giving a breakdown.

Initial information shows the foreigners entered Iraq from neighboring Kuwait, Syria and Jordan, the official said, adding that they belong to the Wahhabi sect of Sunni Islam.

"They are all connected to al-Qaeda," the official said.

Wahhabism is the strict, fundamentalist branch of Sunni Islam from which al-Qaeda leader Osama bin Laden draws spiritual direction. Based in Saudi Arabia, its followers show little tolerance for non-Wahhabi Sunnis and Shiites.