BAGHDAD — A pair of bombs blasted through security checkpoints ringing the Iraqi holy city of Karbala Thursday and killed at least 51 people, many of whom were Shi'ite 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 Shi'ite 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 Shi'ite neighborhood 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, a 42-year-old truck driver. "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."
Still, Mr. Khamas said, the pilgrims continued to head to Karbala: "It will not deter us from continuing our march to the holy shrine ... even if the explosions increase."
The religious rituals mark the end of an annual 40-day mourning period observing the seventh-century death of Imam Hussein, the grandson of the Prophet Muhammad. Imam Hussein is one of the most revered figures among Shi'ite Muslims and was killed in Karbala in a battle that sealed Islam's historic Sunni-Shi'ite split.
Iraqi security officials initially said both bombs in Thursday's attack were planted along the highway that pilgrims were using to walk to Karbala. A police official later said the blasts might have been the work of suicide bombers or explosives-packed cars.
Such confusion is common immediately after large-scale attacks. The officials spoke on the condition of anonymity because they were not authorized to release the information.
The bombings were the latest in a three-day barrage of attacks across Iraq that have killed more than 100 people since Tuesday.