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.

According to some reports, the petrol station was completely destroyed. Local security official Falah-al-Radi told the BBC he expected the death toll to rise.

Last week, six Isis fighters were confronted by security forces on their way to Karbala – five were shot dead while another blew himself up, killing eight civilians.

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 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 religious events. The final stage traditionally involves several days of walking from Basra to Karbala.

The time to reach a settlement in Iraq is now

Minister for the Middle East, Tobias Ellwood, said in response to the attacks: “I utterly condemn the shocking attack on a petrol station and restaurant at al-Hilla earlier today, for which Daesh [Isis] has claimed responsibility.

“The UK continues to stand shoulder to shoulder with the government and people of Iraq in the fight against terrorism. Such an attack shows the desperation of Daesh as they see their so-called caliphate crumble around them.

“My thoughts are with the family and friends of those who have been killed and injured in such a horrific act.”

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 front lines in the six-week-old coalition operation to retake the northern city of Mosul.