A car bomb killed six people and wounded 12 in the holy Iraqi Shia city of Karbala on Monday as hundreds of thousands of pilgrims streamed in for a religious rite, an Iraqi army captain said.
The bomb exploded in a car park on the outskirts of the city where pilgrims heading into Karbala for the annual Arbain event had parked their vehicles, said the officer, asking not to be identified.
"It's difficult for us to control every inch of the province. There are waves of pilgrims," the army captain said when asked how the bomb had gotten through a security cordon of 120,000 police and troops deployed to protect the pilgrims.
Other sources provided conflicting tolls and accounts.
Nusaif Al-Khattab, deputy head of the Karbala provincial council, said five people were wounded.
A hospital source, who asked not to be identified, said the blast killed two people and wounded 13, while a police source said one person was killed and three wounded. He said the explosion was caused by a defective gas cylinder, not a bomb.
Iraq has been rocked by a series of blasts in recent days ahead of the culmination of Arbain, a major Shia rite that has been regularly targeted by Sunni Islamist groups like Al-Qaeda since the 2003 fall of Sunni dictator Saddam Hussein.
Car bombs in and around Baghdad on Sunday killed six people and wounded 29. More than 110 Shia pilgrims, police recruits and police were killed in three days of car bomb and suicide bomb attacks in Karbala and mainly Sunni areas north of Baghdad before that.
The attacks pose a challenge to Iraqi security forces and Prime Minister Nouri Al-Maliki's newly appointed Shia-led government as US troops prepare to stage a full withdrawal this year.
Overall violence in Iraq has fallen sharply since the peak in 2006/07 of the sectarian carnage unleashed after the 2003 US-led invasion. But bombings and shootings carried out by Sunni Islamist insurgents, groups allied to Saddam's former Baath party or Shia militias continue on a daily basis.
Arbain, which culminates on Tuesday, marks the end of a 40-day mourning period for Imam Hussein, a grandson of the Prophet Mohammad and a central figure of Shia Islam. Imam Hussein was killed in a 7th Century battle and his followers believe he was buried in Karbala.
The annual Arbain pilgrimage draws hundreds of thousands, if not millions, of Shia Muslims from Iraq, neighbouring Iran and other Shia communities in the Muslim world. Sunni Islamists like Al-Qaeda view Shias as apostates.
Shia religious events were banned in Iraq under Saddam.