An Isis truck bomb at an Iraqi petrol station where buses filled with Shia pilgrims were parked has killed at least 80 people.
Only ten Iraqi nationals were among the victims, and many were Iranian visitors returning from the Arbaeen ceremony in Karbala, Iraqi security officials said on Thursday, although details on the identities of the dead are still emerging.
There has been an upswing in suicide and car bombs targeting civilians in Iraq since coalition forces began the operation to drive Isis out of the northern city of Mosul last month.
Isis was quick to claim the attack, the violence a stark reminder of the group's ability to inflict death and destruction even as their hold on territory in Iraq and Syria crumbles.
Iraqi police had stepped up security around the annual Arbaeen commemoration amid fears that Isis would target the estimated 17-20 million Shia visitors who descended on Karbala, 60 miles (100 kilometres) south of Baghdad last week.
The holy city is home to the tomb of Imam Hussein, and Arbaeen, which takes place a month after Ashoura, is one of the world's largest religous events. The final stage traditionally involving several days of walking from Basra to Karbala.
Around 25,000 security forces members were deployed to guard both pilgrims and the shrine itself in the town south of Baghdad, but many have since returned to the frontlines in the six-week-old coalition operation to retake the northern city of Mosul.
This year's commoration passed with fewer violent incidents that has been seen previously.
