A man mourns at the site of a suicide truck bomb attack that killed dozens of people near the city of Hilla, south of Baghdad, on Nov. 24. (Alaa Al-Marjani/Reuters)

At least 70 people were killed on Thursday, most of them Shiite Muslim pilgrims from Iran, when an explosive-laden tanker truck detonated at a gas station south of Baghdad in an attack claimed by the Islamic State, according to Iraqi officials.

The bombing was the deadliest in Iraq since July, when a suicide bomber killed more than 300 people in Baghdad, the capital.

The explosion on Thursday, near the town of Hilla, ripped through vehicles transporting people who had completed the annual Arbaeen pilgrimage and were on their way home to Iran, according to Falah Abdulkarim, the head of the security committee for the local provincial council.

The U.S. State Department issued a statement condemning the attacks as “another” example of the militants’ “contempt for human life and its efforts to sow discord and division among the Iraqi people.”

The attack came as Iraqi forces are battling for control of the city of Mosul, in northern Iraq, which has been held by the Sunni Muslim jihadists of the Islamic State for more than two years. The militants have repeatedly tried to carry out large-scale attacks in other parts of the country during the five-week offensive in an attempt to divert the attention of thousands of Iraqi and Kurdish soldiers tightening a cordon around Mosul.

In one such attack, dozens of militants stormed Kirkuk, east of Mosul, and killed more than 80 people, most of them civilians. Last week, a group of Islamic State fighters briefly occupied a village south of Mosul, and on Wednesday, more than a dozen people were injured in a string of bombings in Baghdad, according to the interior ministry.

[Islamic State is kidnapping thousands of people to use as human shields]

The attacks have added to a staggering civilian toll during the battle for Mosul, which began in mid-October. As the Islamic State has retreated from villages on the city’s outskirts, officials have discovered several mass graves containing hundreds of bodies, most of them policemen or soldiers executed by the jihadists as Iraqi government forces approached.

Civilians have also been dying in growing numbers in the city itself as fighting has intensified in Mosul’s eastern neighborhoods. The militants have held civilians as human shields and fired on fleeing residents. At the same time, trauma medics remain positioned too far from the front lines to save many of the critically injured.

Shiite pilgrims in Iraq have been a frequent target of Sunni militants. The attack on Thursday came at the end of Arbaeen, a central Shiite ritual that draws millions of pilgrims each year and commemorates the end of 40 days of mourning for the martyrdom of Imam Hussein at the shrine bearing his name in the city of Karbala.

Iraqi security officials said the explosives — 500 liters of ammonium nitrate — were stashed in a tanker truck that exploded at a gas station east of Hilla. At the time, several vehicles carrying pilgrims, including a large bus, were at the station, according to Abdulkarim, the local security official. The vehicles had recently left Karbala and were taking pilgrims toward the border with Iran, officials said.

Read more:

ISIS driven from ancient Nimrud, where destruction is ‘worse than we thought’

Iraqi Christians, scarred by Islamic State’s cruelty, doubt they will return to Mosul

A walk down one of Baghdad’s most bombed streets

Today’s coverage from Post correspondents around the world

Like Washington Post World on Facebook and stay updated on foreign news