At least 80 Shia pilgrims were killed near Baghdad on Thursday in a truck bombing for which the Islamic State claimed responsibility. The blast tore through a crowded petrol station full of buses carrying Shia pilgrims back from a religious commemoration in Karbala. The religious ceremony, Arbaeen, is one of the world’s largest religious events. Iraqi authorities had boosted security during the event, deploying about 25,000 soldiers. But many of them were sent back to the frontlines of Mosul in recent days. The attack, about 75 miles outside of Baghdad, claimed mostly Iranians as victims in what is being described as a revenge attack for the Mosul operation against ISIS. The terrorist group was quick to claim responsibility, posting a statement that said a bomber “blew up his vehicle amidst their assembly, inflicting among them more than 200 killed and wounded, including Iranians.” Witnesses at the scene said there were at least 20 people injured in the explosion.