A pair of bombs blasted through security checkpoints ringing the Iraqi holy city of Karbala Thursday and killed at least 50 people, many of whom were Shia pilgrims headed to observe yearly religious rituals.

Authorities estimated as many as 175 people were injured in the afternoon blasts, at least one of which appeared to be caused by a car bomb.

There was no immediate claim of responsibility for the attacks. But they bore the hallmark of Al-Qaeda and other Sunni-dominated extremist groups that frequently target Shia pilgrimages in hopes of re-igniting sectarian violence that brought Iraq to the brink of civil war just a few years ago.

Ali Khamas, a pilgrim from the Shia neighbourhood of Sadr City in Baghdad, said he saw a car speeding toward one of the checkpoints, its driver refusing to stop despite warnings screamed by Iraqi soldiers.

“He sped up and blew up his car near the checkpoint,” said Mr. Khamas. “After the explosion, people started to run in all directions, while wounded people on the ground were screaming for help. I saw several dead bodies on the ground.”

The bombings were the latest in a three-day barrage of attacks across Iraq that have killed more than 100 people since Tuesday.

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