Four men have been arrested in connection with a car bomb outside Iraq's holiest Shi-ite shrine which killed at least 95 people including a leading cleric.
According to an Associated Press report the men had connections to al-Qaeda and said they wanted to "keep Iraq in a state of chaos".
The bomb, which also wounded more than 140, detonated outside the Imam Ali mosque in Najaf as Ayatollah Mohammed Baqir al-Hakim emerged after delivering a sermon calling for Iraqi unity. The attack was viewed by many as an assassination.
"Our leader al-Hakim is gone. We want the blood of the killers of al-Hakim," a crowd of 4,000 men beating their chests chanted in unison in Najaf, 110 miles south-west of Baghdad.
The bombing was certain to complicate American efforts to pacify an increasingly violent Iraq. A moderate cleric, al-Hakim was seen as a stabilising force in Iraq. He repeatedly asked the country's Shi-ite majority to be patient with the United States.
Mr Paul Bremer, the US occupation's co-ordinator for Iraq, was out of the country on holiday and had no plans to return early because of the bombing, his office said today, adding he had been in contact. The US-led coalition is responsible for overall security in Iraq.
Mr Bremer left Iraq about a week ago and wasn't expected to return until sometime next week, but precise dates were not released for security reasons, said Mr Jared Young, a spokesman at the Coalition Provisional Authority.
Tens of thousands of worshippers were expected to fill the shrine and the surrounding streets for a funeral service for al-Hakim and other blast victims later today. The main road leading to the shrine was open only to pedestrians, and residents were seen carrying coffins on the tops of cars and backs of trucks for the funeral service.
No Iraqi police or US soldiers were seen in the city centre this morning. While many here blamed the attack on the Sunni Muslim followers of Saddam Hussein, there has been inter-Shi-ite violence recently in Iraq.
Najaf is the headquarters of Iraq's most powerful Shi-ite rivals, including followers of Grand Ayatollah Muhammad Ishaq al-Fayyad, Ayatollah Ali Hussein al-Sistani and Moqtada al-Sadr. Shi-ites make up about 60 per cent of Iraq's population.