The death toll in the stampede over a Tigris River bridge in Baghdad today may reach 1,000, health officials in the Iraqi capital said.
"An hour ago the death toll was 695 killed, but we expect it to hit 1,000," Dr Jaseb Latif of Iraq's Health Ministry Ali said.
The stampede occurred after rumours a suicide bomber was about to blow himself up in the middle of a crowd that had been heading to the Kadhimiya mosque in the old district of north Baghdad for a religious ceremony.
"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."
A Health Ministry official said "hundreds and hundreds" were dead and injured. "We can't tell how many are dead."
An Iraqi woman mourns a dead relative in the makeshift morgue
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.
The crowd was celebrating the martyrdom of Musa Al-Kadhim, a revered religious figure among Shias. Arab television channels showed footage of several bodies partially covered in white sheets on a hospital floor.
Prime Minister Ibrahim Jaafari declared three days of mourning, state television reported.
The streets leading to the mosque are narrow, making it almost impossible for rescue workers to reach the dead and injured in the packed throng, and raising the possibility that the death toll could rise further, witnesses said.
The Kadhimiya mosque is a major Shia shrine in an old district of north Baghdad. The crowd was celebrating the martyrdom of Musa Al-Kadhim, a revered religious figure among Shi'ites.
A series of explosions were heard across Baghdad on this morning.
One correspondent reported hearing six mortar rounds exploding near the international airport, although the US military had no information of any attacks there.
Parliament completed work on the draft text of the constitution on Sunday, but it must be approved by a popular mandate before October 15th to come into force.