Gunfire erupted Thursday while protesters marched toward the bridge where nearly 1,000 Shiites (search) were killed in a stampede during a religious procession, and thousands of people flocked to bury their dead from the tragedy.

Government critics, meanwhile, blasted their leaders for failing to prevent the disaster.

Three people were injured in the latest melee, which triggered an exchange of fire between rival neighborhoods over the Tigris River (search) and underscored yet again the inability of the Iraqi security forces to provide order.

Police said the trouble started when Shiites in the Kazimiyah (search) district approached the bridge from their side, shouting slogans protesting the Wednesday deaths.

No one had told the Iraqi soldiers guarding the bridge about the demonstration, so they started shooting in the air, police said. The three injured were hurt in the ensuing panic.

At the same time across the river in the Sunni neighborhood of Azamiyah (search), unidentified gunmen in several cars opened fire toward the bridge linking the two districts, police said. Residents in turn opened fire at the gunmen.

With all the shooting, gunmen on each side of the river thought they were under attack from the other. They started firing across the river, pinning down people on the bridge.

The shooting continued for about a half hour, police said.

Meanwhile, Iraq's nascent air force carried out its first military mission when it flew two battalions of Iraqi troops into a troubled zone in the north of the country, a U.S. military spokesman said Thursday.

Maj. Gen. Rick Lynch said that three C-130 Hercules cargo planes this week redeployed troops belonging to the 2nd Iraqi Division from the Kurdish city of Irbil to Tal Afar near the country's northwestern frontier with Syria.

"This was the first use of the Iraqi air force," Lynch said.

Wednesday's disaster on a bridge in north Baghdad appeared to have been sparked by a rumor that a homicide bomber was among the more than 1 million people gathering at a Shiite shrine in the capital.

Prime Minister Ibrahim al-Jafaari, who visited a hospital where many of the victims were taken, said neighboring countries such as Jordan and Iran had offered to help treat the victims.

"We are ready to send abroad any patient who needs medical treatment there," he said.

Most of the victims on Imams bridge were trampled or crushed in the stampede. Others plunged 30 feet into the muddy Tigris River. The majority killed were women and children, officials said.

Iraq's Ministry of Interior announced Thursday that 953 people had died and 815 were injured in the crush. But Health Ministry spokesman Qassim Yahya on Thursday said 843 had been killed and 439 injured. It was not possible to reconcile the two.

Critics said the authorities were to blame for a fumbled response to the disaster.

"This is a result of the inadequate performance of the interior and defense ministers, which has caused such a loss of life," said Baha al-Aaraji, a Shiite lawmaker affiliated with radical cleric Muqtada al-Sadr.

"They should stand in front of the national assembly and be questioned. If it is proven that they have failed to fulfill their responsibilities, they should be dismissed and stand trial," he said.

President Jalal Talabani, a Kurd, told state-run Iraqiya TV that "the government should take measures for an honest investigation to determine how failures doubled the casualties."

The tragedy occurred during the annual commemoration of the death in the year 799 of Imam Moussa ibn Jaafar al-Kadhim, one of the 12 principle Shiite saints. He is buried in a mosque in the nearby neighborhood of Kazimiyah.

In Baghdad's Medical City hundreds of people were searching for their dead relatives. Many of the bodies were strewn on the floor outside the hospital's morgue, which itself was packed with corpses.

Crowds also gathered at the Imam Ali Hospital in Baghdad's eastern Sadr City district. Dozens of bodies were identified and taken away for burial by their relatives, medical workers said.

Most of the inhabitants of the impoverished district are Shiites who have moved to the capital from the countryside in the past several decades.

Many families erected large tents on Sadr City streets — a traditional venue for mourners to come to pay respect to the dead.

Some of the dead were taken to Wadi al-Salam, or The Valley of Peace, a cemetery in the southern city of Najaf. Shiites believe that burial there, close to the shrine of Imam Ali, a 7th century Shiite saint, will bless the souls of the dead and secure their passage to heaven.

Since the 2003 ouster of Saddam Hussein, a Sunni, the Shiite political parties have encouraged huge turnouts at religious festivals to display the majority sect's power in the new Iraq. Sunni religious extremists have often targeted the gatherings to foment sectarian war, but that has not stopped the Shiites.

The services have often been chaotic, with huge crowds overtaxing the ability of police and security services to protect them. Television reports said about 1 million pilgrims from Baghdad and outlying provinces had gathered near the shrine on Wednesday.

Even before the stampede, the crowd had been on edge because of the 110-degree heat, a mortar barrage near the shrine where they were headed, and the ever-present fear of homicide bombers, etched into memories after repeated attacks against large religious gatherings.

Police later said they found no explosives at the bridge — either on any individual or in any cars parked nearby. Instead, poor crowd control and the climate of fear in Iraq after years of bullets, bombings and bloodshed appeared largely to have caused the horrific carnage.

Marchers jammed up at a checkpoint at the western edge of the Imams bridge, which has been closed to civilians for months to prevent movement by extremists between the Shiite neighborhood of Kazimiyah and the Sunni district of Azamiyah across the river.