US authorities in Iraq woke up to a brutal new reality yesterday: a significant portion of the country's Shia majority have rebelled against them, with normous potential for death and destruction.
Though casualty figures varied, at least 48 Iraqi Shia and 12 Americans are known to have been killed in 24 hours of clashes from Sunday to Monday, most of them in the Shia slums of Sadr City, north Baghdad.
Cities in the south of the country - Basra, Amara and Najaf - have also seen protests by Shias against the US occupation, some of which turned violent.
Residents of Sadr City expressed strong support for the radical cleric Sheikh Moqtada al-Sadr, who has been the leading Shia critic of the US. Clusters of US tanks were at main intersections and government buildings. The presence of small boys taunting the tank gunners and burning tyres in the rubbish-strewn boulevards made north Baghdad resemble the Gaza Strip yesterday .
US forces also clashed with Shia muslims in the Baghdad neighbourhood of Shuala, where Apache helicopters fired missiles at a building used by Sheikh al-Sadr's group. Iraqi radio reported two were killed there. It was the first such attack since last year's war.
"It was like a war here between Mehdi's Army and the Americans," a 21-year-old named Haidar told The Irish Times. "The shooting never stopped for 12 hours. All of us are in Mehdi's Army. To be a member means I am ready to be a martyr, and I am fighting for my religion."
Mehdi's Army is the name that Sheikh al-Sadr has given his grouping of uneducated young men, many of whom looted Baghdad following the US invasion.
Though their confrontation is in danger of spinning out of control, both Sheikh al-Sadr and US authorities continued the verbal escalation.
The Coalition Provisional Authority (CPA) dredged up an arrest warrant for the young cleric first issued last year, accusing him of involvement in the stabbing to death of Abdul-Majid al-Khoei, the son of an ayatollah. Al-Khoei had just returned from exile in London, and was considered pro-US.
One of Sheikh al-Sadr's top aides is already being held in connection with the murder, which occurred in one of Shia Islam's holiest shrines in Najaf.
Sheikh al-Sadr is holding a sit-in in his mosque in Kufa, near Najaf, and CPA spokesman Mr Dan Senor said his arrest would be "without advance warning".
Speaking to a ministerial committee of the US-appointed Iraqi government, the US administrator, Mr Paul Bremer, said Sheikh al-Sadr's group had "basically placed itself outside the legal authorities..."
Sheikh al-Sadr responded with a statement that was read in his mosque in Kufa. "I am accused by one of the leaders of evil, Bremer, of being an outlaw. If that means breaking the law of the American tyranny and its filthy constitution (for Iraq), I am proud of that, and that is why I am in revolt."
And last night the young cleric rejected a call by moderate Shia leaders to renounce violence.
"He insists on staying on the same course that could destroy the nation," said an aide to Mohammad Bahr al-Uloum, a member of the US-installed Iraqi Governing Council.
Mr Bremer has promised to avenge the deaths of four former special forces officers who worked as security agents for the CPA. They were lynched in Fallujah, west of Baghdad, last week.
US forces have cut the road between Fallujah and Amman and imposed a curfew.
A US marine and seven Iraqis were reported killed in further clashes in Fallujah yesterday.
And in an ominous development for coalition forces, a document circulating in Sadr City yesterday presaged a new alliance of Sunni and Shia against their occupiers.
"From the people of Fallujah," it began. "We hail Moqtada Sadr and the heroic stand of the people of Sadr City and what they did ... to get rid of the occupiers. We will work together to destroy the infidels."