Dozens of pilgrims were killed on Tuesday after a stampede during Ashura commemorations in the Iraqi city of Karbala.
The stampede happened when part of a walkway collapsed during the ceremony at the shrine of Imam Hussein, security officials told AP.
At least 31 people died and at least 100 others were injured in the crush "towards the end of the Ashura ritual, causing panic and a stampede", Health Ministry spokesman Saif Al Badr said, adding that the toll was expected to rise.
Ten of those hurt in the incident suffered severe injuries, Mr Al Badr said.
But a Karbala security official said that overcrowding was the cause of the stampede, rather than the walkway collapse.
"People were pushing each other which resulted in the stampede and the death and injury of many pilgrims," he said.
There is, as yet, no official confirmation on the cause but medical teams are on scene treating the injured.
Pilgrims walk around Karbala to commemorate the death of Hussein, Prophet Mohammed's grandson, during a major battle near the city in 680 CE.
Crowds gather at the shrine of Hussein to commemorate his death.
They converge on the holy city on the 10th day of the lunar month of Muharram.
The incident took place during the tweireej run, when tens of thousands of people run towards the shrine of Hussein in Karbala about noon.
The two-kilometre run symbolises the moment maternal cousins of Hussein’s half-brother Al Abbas ran from the nearby village of Tweireej to help him only to find out that he had died.
Tuesday's incident happened due to “some sort of an obstacle that developed from someone falling over or something to that nature that resulted in a bottleneck and a stampeded", said a religious figure in Baghdad.
"The venue is big but when so many people turn up with no proper precautions taken it becomes small and the risk rises," he said. "Carelessness is the norm in Iraq."
Ashura is a national holiday in Iraq and devoted pilgrims travel from neighbouring countries such as Iran, Pakistan and India to mark it in Iraq.
On Tuesday streets across the country were shut to allow for the funeral-style processions and re-enactments of the Battle of Karbala.
Similar ceremonies took place in the capital Baghdad, in the southern city of Basra and in Iraq's second holy city Najaf, where the Prophet Mohammed's son-in-law Ali is buried.
In 2005, at least 965 pilgrims heading to the Imam Kadhim shrine in Baghdad during a different holiday died after rumours of a suicide bomber in the crowd sparked a mass stampede.