Millions of Shiite pilgrims on Sunday celebrated the anniversary of the birth of the Messiah-like Imam al-Mahdi amid heightened security in the Shiite holy city of Karbala. The number of visitors reached its peak on Sunday, with 2 million pilgrims pouring into the city, located some 110 kilometres south- west of Baghdad. Shiite pilgrims visit Karbala to commemorate the birth of the 12th Imam, the dpa reported. A total of 50,000 security personnel have been deployed in the area. The Iraqi Air Force carried out reconnaissance flights over the city before and during the pilgrimage, while the US Air Force secured the area around the city. A team of 2,000 female guards were also deployed to counter the growing trend for the terrorists to use women for suicide bomb attacks. While the Sunday pilgrimage was safe, the road to Karbala remained deadly. On Saturday, an attack that targeted Shiite pilgrims boarding minibuses in Baghdad left six civilians dead and 11 wounded. Another bombing occurred Friday night, in which at least nine pilgrims were killed and 40 injured when a car bomb ripped through a bus station in the district of Balad in Salaheddin province, 90 kilometres north of Baghdad. The deadliest attack came on Thursday, when at least 20 people were killed and around 100 injured in the Iskandariya district 40 kilometres south of Baghdad as two women suicide bombers wearing explosive belts blew themselves up among a group of pilgrims. Shiite pilgrims have been a constant target for extremist Sunni Muslim groups operating in Iraq, mainly al-Qaeda, during their annual religious celebrations.