More than 80 people are dead, most of them Iranian Shi'ite pilgrims, after a suicide truck bomber detonated at a petrol station in the city of Hilla 100 km south of Baghdad, police and medical sources say.
Islamic State (IS), the ultra hardline Sunni militant group that considers all Shi'ites to be apostates, claimed responsibility for Thursday's attack in an online statement.
The pilgrims were en route back to Iran from the Iraqi Shi'ite holy city of Kerbala, where they had commemorated Arbaeen, the 40th day of mourning for the killing of Imam Hussein, a grandson of the Prophet Mohammad, in the 7th century AD, the medical sources said.
The gas station has a restaurant in its premises that is popular with travellers. Five pilgrim buses were torched by the force of the blast from the explosives-laden truck, a police official said.
Islamic State has intensified attacks over the past month in areas out of its control in efforts to weaken a US-backed military offensive launched on October 17 to retake Mosul, the last major city under IS control in Iraq.