MOSUL, Iraq — The death toll from a car bombing south of Baghdad claimed by the Islamic State group rose to 73 today, including about 40 Iranian pilgrims, as Iraqi forces continued to inch closer to the center of the northern city of Mosul in street-to-street fighting east of the Tigris River.

Iraqi police and hospital officials said 65 other people were wounded in the Thursday night attack at a gas station on a major highway near the city of Hilla.

It was the deadliest IS attack in Iraq since July, when a car bomb killed about 300 in a commercial district in Baghdad.

IS claimed the attack in a brief statement on its Aamaq media arm, saying it was a suicide truck bomb. Earlier, Iraqi officials had put the death toll at 56.

The attack appears to have targeted a bus with Iranian pilgrims heading home after a major Shiite religious observance in the holy city of Karbala.

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

The attack came a day after some dozen 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 IS or its forerunner, al-Qaida in Iraq, and which mostly targeted members of Iraq’s Shiite majority.

The gas station bombing underlined the continuing ability of IS to stage high-profile terror attacks even as a massive Iraqi military operation is under way to dislodge its fighters from Mosul, its last major urban stronghold in Iraq. The offensive is aided by volunteer militiamen and the U.S.-led coalition, which has mostly been pounding IS targets in Mosul with airstrikes.

Moreover, Thursday’s IS bombing took place in Iraq’s Shiite hinterland south of Baghdad, a region that has largely been spared the near-daily violence that has engulfed the capital and Sunni regions.

Earlier this week, Prime Minister Haider al-Abadi visited Karbala, where he praised the country’s security forces for protecting the pilgrims.

Extremist Sunni militants, including the Islamic State group, view Shiites as heretics and routinely target Iranian pilgrims who visit Iraq.