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Some 77 people, most of them Shia pilgrims from Iran and Afghanistan, have been killed in a truck bomb attack in Iraq, officials say.

The blast struck at a petrol station and restaurant near Hilla, some 100 km (60 miles) south of Baghdad.

Busloads of pilgrims had stopped there on their way home from commemorating Arbaeen in the holy city of Karbala. Some 40 people were wounded.

The jihadist group Islamic State said it carried out the attack.

A senior local police officer told the ´óÏó´«Ã½ that the victims were on board four buses filling up with fuel at the road stop near the village of Shomali, 80 km (50 miles) south-east of Karbala.

A truck loaded with ammonia nitrate and other explosive material as well as fuel had been parked at the petrol station, and caused massive damage when it was detonated.

Pictures from the scene showed dense black smoke and the wreckage of minibuses and cars. The restaurant and petrol station also appeared to have been destroyed. Bodies were strewn on the highway.

It is a familiar tactic of IS militants to strike in one place when under pressure in another, says the ´óÏó´«Ã½ Middle East correspondent Orla Guerin. Iraqi forces are currently pounding the IS-stronghold of Mosul in northern Iraq.

Millions of Shia pilgrims travelled to Karbala to mark Arbaeen, the end of the 40-day mourning period for the third Shia Imam, Hussein. This year it took place on Sunday.

Hussein, the grandson of the Prophet Muhammad, was killed in battle at Karbala in the 7th Century on a day that is known as Ashura. His martyrdom is considered a defining event in the Sunni-Shia schism.

The Sunni militants of IS regard Shia as apostates because of their veneration of the Prophet's family and other beliefs and practices.

Shia pilgrims are a target at this time of year, our correspondent adds. Although around 25,000 security forces were deployed to Karbala for the festival, some had returned to the front lines.

Last week six IS militants were confronted by security forces while on their way to Karbala, official said. Five were shot dead but the sixth blew himself up, killing eight civilians.

28 February: Twin suicide bomb attacks hit market in Sadr City, killing 70

6 March: Truck bomb at checkpoint at entrance to Hilla kills 47

11 May: Car bombs in Baghdad kill 93 people, including 64 in market in Shia district of Sadr City

2 July: Truck bombing outside shopping centre in mainly Shia Karrada district of Baghdad kills more than 300