HILLA, Iraq -- A car bomb tore through a gas station south of Baghdad on Thursday, killing at least 56 people, including 20 Iranians, in an attack claimed by the Islamic State group.

Police and hospital officials confirmed the toll and said another 45 people were wounded in the attack, which almost completely destroyed the gas station, several nearby stores and set several cars on fire. The station is located on a major highway.

The blast knocked out power at the station, forcing relatives looking for the remains of loved ones to use the glare of their mobile phones to guide them. Body parts that remained unclaimed were gathered in a blue bag and placed on the sidewalk outside the station. Large sections of the station were covered in blood.

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Iran’s Deputy Foreign Minister Hassan Qashqavi was quoted by the semi-official Tasnim news agency as saying that 80 people were killed, including 40 Iranians. Conflicting death tolls are common in the aftermath of large attacks.

The Islamic State group claimed the attack in a brief statement carried by its Aamaq news agency, saying it was a suicide truck bomb.

The Iraqi officials said the target of the attack appears to have been a bus carrying Iranian pilgrims heading home after taking part in a major Shiite religious observance in the holy city of Karbala. The blast left the bus and some dozen cars charred.

The Shiite observance marks the 40th day after the death anniversary of a much revered, 7th century imam. It routinely attracts hundreds of thousands of pilgrims, including many Iranians who travel overland into Iraq for the occasion.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

Thursday’s attack came a day after several small-scale bombings in and around Baghdad killed 31 people and wounded more than a 100, a particularly bloody day even by the standards of the Iraqi capital, which has for more than a decade endured near-daily violence blamed on ISIS or its forerunner, al-Qaida in Iraq.

In northern Iraq, meanwhile, troops drove ISIS militants from three more neighborhoods in Mosul, the country’s second largest city, where U.S.-backed offensive has been underway for more than six weeks.

Brig. Gen. Haider Fadhil of the special forces told The Associated Press his men have retaken the neighborhoods of Amn, Qahira and Green Apartments and were expanding their foothold in the densely populated district of Zohour.

The neighborhoods are all east of the Tigris River, where most of the fighting has taken place. A U.S.-led coalition is carrying out airstrikes to support the troops.

Prime Minister Haider al-Abadi meanwhile flew to an airstrip outside the town of Tal Afar, to the west of Mosul, on a previously unannounced visit on Thursday, according to footage aired by the state-owned Iraqiya television network. The airstrip was seized from ISIS by state-sanctioned Shiite militiamen earlier this week.