BAGHDAD: Thousands of police backed by helicopters patrolled Iraq's holy city of Karbala on Friday, assigned to prevent attacks against hundreds of thousands of Muslims observing an annual pilgrimage, officials said.    

Bombings at another pilgrimage last month killed more than 100 people, part of a fierce and sustained terror campaign blamed on Al Qaeda-linked insurgents seeking to destabilise the government and stoke sectarian tensions six months after the withdrawal of last US troops.

The threat of violence did not stop the throngs of white-robed pilgrims, who crowded in and around Karbala's golden-domed main shrine.

Vehicles have been banned inside Karbala, 80 kilometers south of Baghdad, since Tuesday, when two car bombs outside a market in the holy city killed five people and wounded 30 others.

More than 40,000 police and soldiers were patrolling the holy city and 14 helicopters were monitoring the crowds and looking out for insurgents, provincial councilman Hussein Shadhan al-Aboudi said.—AP