BASRA - A suicide bomber killed 53 people in an apparent sectarian attack in southern Iraq Saturday casting a pall over the climax of a Shia pilgrimage that draws hundreds of thousands from around the world.

The attack on Shia devotees on the outskirts of the port city of Basra, which left 137 wounded, came with Iraq mired in a political row that has pitted the Shia-led government against the main Sunni-backed bloc and stoked sectarian tensions less than a month after US forces completed their pullout.

The violence was the latest in a spate of attacks against Shia pilgrims in the two weeks leading to the conclusion of Arbaeen, which marks 40 days after the Ashura anniversary commemorating the slaying of Hazrat Imam Hussein.

The bombing killed 53 people and wounded 137, according to Riyadh Abdulamir, head of Basra province’s health department. He said women and children were among the casualties, but did not give further details.

The death toll was the highest since attacks on Shias in Baghdad and southern Iraq killed 70 people on December 5.

The attacker, who had been distributing cake and other food to pilgrims walking to the Khutwa Imam Ali, a site on the outskirts of Basra venerated by believers for its associations with one of the key figures of their faith, blew himself up near a security checkpoint.

“I saw a soldier take hold of the attacker to take him to the officer in charge,” said Kadhim Nasser, who was in charge of a nearby rest stop for pilgrims.

“As he was pushing him, something happened and the soldier fell to the ground.”

“Immediately, he blew himself up. When he did that, women and children were passing by. I saw dozens of women and children among the wounded,” the 42-year-old added.

Pilgrims in southern Iraq who cannot visit the central shrine city of Karbala to mark Arbaeen typically make the shorter trip to Khutwa Imam Ali, which lies around 12 km west of Basra.

Hundreds of thousands did make it to Karbala on Saturday amid massive security in face of the insurgent threat.

Officials said 15 million pilgrims have passed through the city in the past two weeks leading up to the end of the commemorations, including some 500,000 from outside Iraq.

Some 35,000 police and troops were deployed to provide security throughout the rituals, with a further two brigades added to protect pilgrims heading home, said Lieutenant General Othman al-Ghanimi, who commands forces across central Iraq.

Among them were 500 policewomen charging with assisting in checkpoint searches, as well as sonar detectors and sniffer dogs.

Ghanimi said no incidents had been reported in Karbala.

Provincial health department spokesman Jamal Mehdi said that hospitals in the shrine city had treated 20,000 pilgrims but that there had been no deaths.