Nine hundred and thirty five people were crushed to death or drowned on Wednesday in a stampede on a Baghdad bridge, triggered by fears that a suicide bomber was among vast crowds of Shiite pilgrims massed for a religious ceremony.
Iraq authorities said the tragedy, which unfolded after a deadly mortar attack on a Shiite shrine, was a "terrorist" act
by toppled dictator Saddam Hussein's loyalists and Al Qaeda frontman in Iraq, Abu Musab al-Zaqrqawi.
Scores jumped or were pushed to their deaths into the muddy Tigris River about 30 feet below, while others were crushed in the crowd. Most of the dead were women and children, Interior Ministry spokesman Lt. Col. Adnan Abdul-Rahman said.
It was the single biggest confirmed loss of life in Iraq since the March 2003 invasion.
Tensions already had been running high in the procession in Baghdad's heavily Shia Kazimiyah district because of a mortar attack two hours earlier against the shrine where the marchers were heading. The shrine was about a mile from the bridge.
Abdul-Rahman said 935 were killed and 322 injured, although figures from other official sources varied slightly. Survivors were taken in ambulances and private cars to several hospitals, where officials scrambled to compile accurate casualty figures.
Prime Minister Ibrahim al-Jaafari, a Shia, declared a three-day mourning period.
Thousands of people rushed to both banks of the river to search for survivors, and bare-chested men jumped in to try to recover bodies.
Scores of bodies covered with white sheets lay on the sidewalk outside one hospital because the morgue was jammed. Many of them were women in black gowns, as well as children and old men.
Sobbing relatives wandered amid the dead, lifting the sheets to try to identify their kin. When they found them, they would shriek in grief, pound their chests or collapse to the ground, sobbing.
Hundreds of thousands of Shias had been marching across the bridge, which links Baghdad's Shia Kazimiyah district with heavily Sunni Azamiyah. They were heading for the tomb of Imam Mousa al-Kadhim, a 9th century Shia saint, about a mile from the span.
Television reports said about 1 million pilgrims from Baghdad and outlying provinces had gathered near the shrine for the annual commemoration of the saint's death.
Interior Minister Bayn Jabr told state-run Iraqiya television that the procession slowed at security barricades about a quarter of the way across the bridge.
"Pushing started when a rumour was spread by a terrorist who claimed that there was a person with an explosive belt, which caused panic," Jabr said. "Some fell from the bridge, others fell on the barricades" and were trampled to death.
The barricades were placed there months ago to keep extremists from both sectarian communities from infiltrating the other's neighborhood.
Police later said they found no explosives -- either on any individual or in any cars parked nearby.
"We were on the bridge. It was so crowded. Thousands of people were surrounding me," said survivor Fadhel Ali, 28, barefoot and soaking wet.
"We heard that a suicide attacker was among the crowd. Everybody was yelling, so I jumped from the bridge into the river, swam and reached the bank. I saw women, children and old men falling after me into the water."
Health Minister Abdul-Mutalib Mohammed told Iraqiya television that "there was many cases of suffocation."
First reports suggested that the bridge's railing collapsed, but TV video showed the green, waist-high railing undamaged.
Shia processions, which can draw huge crowds, are often targeted by Sunni extremists seeking to trigger sectarian war, so worshippers are on guard for trouble.
Mortar shells had exploded in the shrine compound about two hours earlier, killing at least seven people. US Apache helicopters fired at the attackers.
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In March 2004 suicide attackers struck worshippers at the Imam Kadhim shrine and a holy site in Karbala, killing at least 181 overall.
The head of the country's major Sunni clerical group, the Association of Muslim Scholars, told Al-Jazeera television that Wednesday's disaster was "another catastrophe and something else that could be added to the list of ongoing Iraqi tragedies."
"On this occasion we want to express our condolences to all the Iraqis and the parents of the martyrs, who fell today in Kazimiyah and all over Iraq," said the cleric, Haith al-Dhari.
Elsewhere, a US soldier was killed Tuesday by a roadside bomb in the city of Iskandariyah, about 30 miles south of Baghdad, the military said.
Eyewitnesses said the town of Qaim, about 200 miles northwest of Baghdad, was quiet and virtually deserted Wednesday after a day of US airstrikes and heavy fighting between the pro-government Bumahl tribe and the pro-insurgent Karabilah tribe.
Iraqi officials said 45 people had died, most in the tribal clashes, during which hundreds of residents fled their homes and took refuge in the surrounding countryside.
The border region is considered a prime infiltration route for smugglers and foreign militants trying to reach central and western Iraq.
This week's violence came amid new twists about Iraq's draft constitution. On Tuesday, U.S. ambassador Zalmay Khalilzad raised the possibility of further changes to the draft charter finalized by the dominant Kurdish and Shia Arab bloc but vehemently opposed by Arab Sunnis who form the core of the armed insurgency.
Sunnis had demanded revisions in the constitution, and Khalilzad's move indicated the Bush administration has not given up its campaign to obtain some sort of Sunni endorsement for the national charter.
Khalilzad said he believed "a final, final draft has not yet been, or the edits have not been, presented yet" -- a strong hint to Shias and Kurds that Washington wants another bid to accommodate the Sunnis before the October 15 referendum.
Shia leaders had no comment on the ambassador's remarks. As constitution wrangling drew to a close last week, Shia officials complained privately that the Sunnis were stonewalling and that further negotiations were pointless.
Khaled al-Attiyah, a Shia member of the constitution drafting committee, insisted Tuesday that "no changes are allowed" to the draft "except for minor edits for the language."
This indicated that the Shias and Kurds would be unlikely to compromise on their core demand for Iraq to be turned into a loose federation. Sunnis fear this would eventually lead to the breakup of the nation which has been ruled as a centralized entity since it was established by British occupiers in the 1920s.
Sunni Arabs form an estimated 20 percent of the population. They could still scuttle the charter because of a rule that states that if two-thirds of the voters in any three provinces reject the draft, it would be defeated.
Even if the Sunnis lose the referendum, a bitter political battle at a time when the Sunni-led insurgency shows no sign of abating could plunge the country into a full-scale sectarian conflict.
The Shia Supreme Council for the Islamic Revolution in Iraq condemned attacks by foreign fighters against "our beloved people" and urged the government to "stop criminals and terrorists from crossing into Iraq."
