Iraqi officials said on Thursday they had defused three car bombs aimed at some of the 7 million pilgrims visiting Kerbala for one of Shi'ite Islam's most important rituals.

Guarded by 40,000 Iraqi police and soldiers backed by tanks, crowds of pilgrims, some beating their heads and whipping themselves, gathered in the holy city to observe Arbain.

Many of the millions travel to the event by foot, providing a stern test for Iraqi security forces after suspected Sunni Arab insurgents killed 149 pilgrims in attacks last year.

Aqeel al-Khazali, the governor of Kerbala, said security forces had defused three car bombs at entrances to the city during the lead-up to Arbain. Despite the risk of attacks, pilgrims said they were determined to attend.

"I lost my hand last year in a bomb blast in Kerbala. I lost my close friends," said Mohammed Abbas, 41 who lives in Kerbala, 110 km (70 miles) south of Baghdad.

"Nevertheless I decided to leave all fears and painful memories behind. I have come to join the rituals to feel I am still alive," he told Reuters.

Arbain marks the end of a 40-day mourning period following Ashura, the religious ritual that commemorates the death of the Prophet Mohammad's grandson Imam Hussein in 680.

Kerbala's wide avenues and backstreets were awash with black-clad pilgrims who waved brightly coloured flags and banners bearing the name of the province from where they came.

Many jostling in processions through the streets were beating themselves with their hands, sticks or metal chains, leaving some with bleeding backs.

Others covered their heads with mud in a display of devotion at the holiest location between the golden-domed Imam Hussein and Imam Abbas mosques in the centre of Kerbala's old city.

Along sidewalks rows and rows of giant cooking pots offered rice and qeema, a traditional Iraqi stew of lentils and minced meat. Carts also served tea and milk, all meals given free.

With all the city's 350 hotels booked out, thousands of pilgrims were forced to sleep in the street. Such rituals have been a target in the past for Sunni Islamist al Qaeda, which considers Shi'ites heretics. Shi'ites form a majority in Iraq but a minority in the Muslim world.

Khazali also said 18 suspects had been arrested, some with documents calling for sectarian violence and for the event, which he said attracted some 7 million people, to be disrupted.

However extra security was unable to prevent a suspected al Qaeda suicide bomber killing 63 Arbain pilgrims in Iskandariya just south of Baghdad on Sunday and there have been at least three other deadly attacks on those heading to the event.

"I was very afraid all along the road to Kerbala. Every moment I expected something bad would happen to us," said Radhi Khaled, a 43-year-old teacher from the southern Maysan province.

Businessman Mubarak Ali, 52, said he had feared the worst when he left his home in Bahrain 30 days ago to attend. "I said goodbye to all my close friends and relatives. The news bulletins we watch every day gives us the impression that everybody who visits Iraq will not come back alive," he said, saying he was astonished at the tight security.

"I am calling all my friends across Gulf countries to visit and see a new Iraq." - Reuters