Up to 40 Shia pilgrims have been killed by a female suicide bomber at a shrine in Baghdad.
Iraqi officials said as many as 72 people were wounded in the blast, in the Kadhimiya area of the Iraqi capital, where pilgrims were gathering for a religious ceremony.
Police said 16 Iranian pilgrims were among those who died. There are fears the death toll will rise.
Processions of Shia pilgrims across Iraq have been targeted by Sunnis in the past.
Police said the suicide bomber detonated her device at a checkpoint outside the Imam Moussa al-Kadhim shrine on Sunday.
The blast happened at about 1100 (0800 GMT) as pilgrims were preparing for the Ashura holiday 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 pilgrims are already flocking to shrines across Iraq. The BBC reports 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.