At least 80 people were killed when a truck laden with explosives hit a group of Shia pilgrims in the Iraqi city of Hilla on Thursday.
The pilgrims were returning from the city of Karbala, where they had commemorated Arbaeen, the 40th day of mourning for the killing of Imam Hussein, the grandson of the Prophet Muhammad.
Falah al-Radhi, head of the provincial security committee for Babylon, the province where the bombing took place, said fewer than 10 of the people killed in the attack were Iraqis and "the rest were Iranians".
Daesh claimed responsibility for the bombing.
Police officials said the pilgrims had stopped at a petrol station in Hilla, some 60 miles south of Baghdad, when the "suicide bomber" rammed his truck into parked buses. Some reports claimed the truck was already parked near the site of the blast before the buses arrived.
The petrol station has a restaurant on its premises where travellers normally stop to have meals. Five of the buses carrying the pilgrims were set alight by the force of the blast, a police official said.
Daesh has intensified attacks in Iraq 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.
Mosul is the last major city under Daesh control in Iraq.