A female suicide bomber has killed at least 35 Shia pilgrims including 16 Iranians near a shrine in the Iraqi capital Baghdad, police say.
As many as 72 people were injured in the blast, in the Kadhimiya area of the Iraqi capital, where pilgrims were gathering for a religious ceremony.
There were fears that the death toll would rise.
Processions of Shia pilgrims across Iraq have been targeted by Sunni insurgents in the past.
Police said the suicide bomber detonated her device at a checkpoint outside the Imam Moussa al-Kadhim shrine on Sunday.
An Iranian pilgrim wept outside a hospital where the injured were taken
"A woman wearing an explosive vest managed to reach one of the security checkpoints near the revered Kadhim shrine and exploded herself among a crowd of pilgrims," Iraqi security official Qassim Moussawi said.
Many of the victims were women and children, another security official told the AFP news agency.
The blast happened at about 1100 (0800 GMT) as pilgrims were preparing for the Ashura commemorations to mourn the death of Imam Hussein, grandson of the Prophet Muhammad, in the 7th Century.
This year, Ashura falls on Wednesday 7 January, but tens of thousands of pilgrims are already flocking to shrines across Iraq.
Hundreds of thousands are expected in Karbala later this week.
Sunday's attack in Baghdad was the second in the area in nine days. At least 17 people were killed in a car bomb in late December.
On Friday, at least 23 people were killed in a suicide bomb attack at a gathering of Sunni Muslim leaders south of Baghdad.
About 110 people were also injured in Yusufiya, 20km (12 miles) from Baghdad.
Sectarian violence in Baghdad has declined over the past year, but religious festivals or ceremonies remain times of heightened tension, the BBC's Caroline Wyatt in Baghdad says.
The worst attacks during Ashura came in 2004, when 170 people were killed and many more hurt in two separate bombings in Kadhimiya and Karbala, presaging the wave of sectarian violence which later swept the country, our correspondent adds.
Iraqi security forces say they are deploying more forces to both sites to keep pilgrims safe.
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