IRAQ– (CNN) At least 57 people — mostly Iranian Shi’ite pilgrims — were killed when a truck bomb exploded at a gas station in Iraq, authorities said.

ISIS, a Sunni terror group, claimed responsibility for the attack in a statement posted online.

The blast happened Thursday on a highway southeast of Baghdad between Babel and Al-Qadisiyyah, said Falah al Radhi, the head of the Babel security council.

Iraq’s Joint Operation Command said 57 people died. Al Radhi said at least 50 people were also wounded.

The parked truck exploded near several buses carrying Shi’ite pilgrims — mostly Iranians — Radhi said. The Iranian pilgrims were in Iraq to commemorate Imam Hussein’s death.

Hussein was the grandson of the Prophet Mohammed. After Mohammed’s death in 632, Hussein was killed during a battle near Karbala for control of the Muslim nation.

Hussein’s 7th-century death led to a split between Sunni and Shi’ite Muslims that still divides the sects today.

During former Iraqi President Saddam Hussein’s rule, the Sunni leader forbade Shi’ite pilgrims from making the journey on foot. But after the US-led invasion toppled the President, the pilgrimages grew in numbers.

In recent years, scores of pilgrims have been killed in attacks blamed on Sunni extremists. Despite ongoing dangers, Shi’ite pilgrims still make the journey to Karbala.

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