BAGHDAD - Nearly 650 Iraqi Shi"ites died in a stampede on a Tigris River bridge in Baghdad on Wednesday, panicked by rumors a suicide bomber was about to blow himself up, an Interior Ministry official told Reuters.

Iraqis walk among shoes lost during a stampede on a bridge in Baghdad. Up to 650 people were crushed to death or drowned in a stampede on a Baghdad bridge triggered by fears a suicide bomber was among vast crowds of Shiite pilgrims massed for a religious ceremony.(AFP/Ahmad Al-Rubaye)

<##IMAGE##>Most victims were women and children who "died by drowning or being trampled" after panic swept a throng of thousands of people heading to a religious ceremony, the official said.

By 2:15 p.m. the death toll had risen to 647, with 301 injured, the official said.

Television images showed people clambering down from the bridge to escape the surging crowd and piles of slippers left behind by the crush of people.

One hospital said it had received at least 100 bodies by 12:30. A hospital source said bodies were also being sent to two nearby hospitals.

A police source said swarming crowds had been heading to the Kadhimiya mosque in the old district of north Baghdad for a religious ceremony when someone shouted there was a suicide bomber among them.

"Hundreds of people started running and some threw themselves off the bridge into the river," the source said.

"Many elderly died immediately as a result of the stampede but dozens drowned, many bodies are still in the river and boats are working on picking them up."

MORTAR ATTACKS

Earlier at least seven people were killed in three separate mortar attacks on the crowd as thousands of people marched to the mosque.

Tensions have been running high between the main religious and ethnic communities ahead of a referendum on a divisive new constitution for the post-Saddam Hussein era.

Parliament completed work on a draft constitution on Sunday and it must be approved by a popular mandate before October 15 to come into force.

The crowd was celebrating the martyrdom of Musa Al-Kadhim, a revered religious figure among Shi"ites.

Reuters Television showed a woman weeping over the body of her dead child in al-Nu"man hospital. Dozens of bodies were strewn across the floor.

The hospital was filled with the sounds of screaming and wailing as disconsolate men and women searched for, and found, loved ones.

Doctors and orderlies were treating many of the injured on the floor or on trolleys in corridors. A child lay unconscious on a stretcher, with an intravenous drip dangling from her arm.

OFFICIAL MOURNING

Prime Minister Ibrahim Jaafari declared three days of mourning, state television reported.

"This is a great tragedy which will leave a scar on our souls ... We pray to God that he will save the souls of our martyrs and help heal the wounded," President Jalal Talabani said in a statement.

Explosions were heard across Baghdad on Wednesday morning.

A Reuters correspondent reported hearing six mortar rounds exploding near the main airport, although the U.S. military had no information of any attacks there.

Despite the draft constitution, there has been no easing in an insurgency waged by Sunni Muslims, dominant under Saddam, and international guerrillas inspired by Osama bin Laden.

The U.S.-led coalition invaded Iraq in March 2003 and has been battling insurgents while Iraqis have tried to form a new post-Saddam constitution and government.

The persistent fighting has helped to push down President George W. Bush"s approval rating to a career low of 45 percent on concerns over the war and soaring fuel prices, according to an ABC News/Washington Post poll published on Tuesday.

The U.S. war in Iraq now costs more per month than the average monthly cost of military operations in Vietnam in the 1960s and 1970s, according to a report issued on Wednesday.

The report, entitled "The Iraq Quagmire" from the Institute for Policy Studies and Foreign Policy in Focus, both liberal, anti-war organizations, put the cost of operations in Iraq at $5.6 billion per month.

This breaks down to almost $186 million a day.

"By comparison, the average cost of U.S. operations in Vietnam over the eight-year war was $5.1 billion per month, adjusting for inflation," it said.

(Additional reporting by Mariam Karouny, Fares Mehdawi, Lutfi Abu Oun, Aseel Kami)