At least 21 people were killed Thursday in a bombing south of Baghdad.
The blast happened outside of a gas station and restaurant near the town of Hilla.
The Islamic State's Amaq news agency tweeted claiming as many as 200 people were killed or wounded in the explosion.
The blast happened while the road was full of people returning from the Arbaeen pilgrimage in Karbala, which is south of Baghdad, according to the BBC.
Officials said the attack appeared to have targeted a bus carrying Iranians who were headed home after observing the major Shiite religious pilgrimage.
The death toll is expected to rise.
Further north, Iraqi troops continued their advance into Mosul.
Brig. Gen. Haider Fadhil of the special forces said Iraqi troops drove Islamic State fighters out of the neighborhoods of Amn, Qahira and Green Apartments.
Each of those neighborhoods is located east of the Tigris River, where most of the fight to regain control of Mosul has taken place.
The Associated Press contributed to this report.