Baghdad was under tight security on Wednesday with roads closed to cars and additional checkpoints set up throughout the capital.
Police announced they had closed bridges leading to the south of the country in effort to block a squad of suicide bombers reported to be heading to Karbala to disrupt the Ashura ceremonies marking the death of the Imam Hussein, a grandson of the Prophet Muhammed.
Security has been heightened across Iraq for the Shiite
festival which reaches its climax Thursday.
As the holiest of Shia occasions, whose commemoration was banned under ousted Iraqi leader Saddam Hussein's regime, Ashura has often been the target of Sunni extremists.
In 2004, 170 people were killed in attacks in Baghdad and Karbala and another 44 died in 2005.
Iraqi boys flagellate themselves
as they take part in the ceremony
In Karbala, security was incredibly tight, with police everywhere conducting random checks, but so far, no untoward incidents were reported.
Search for explosives
Around 8000 security personnel have been deployed in and around Karbala to ensure the smooth passage of the Shia ceremony on Thursday, while the government has declared a two-day holiday from Wednesday.
Police went through the hotels housing pilgrims and visitors and searched belongings for any explosives.
Near the shrine of Imam Hussein, police commandos searched worshippers from head to toe, even removing their keffiyahs, the traditional Arab headdress.
Separate tents have been set up at checkpoints to search women as well.
Despite the security measures, Iraq's minister of higher education survived a car bomb attack in Baghdad on Wednesday, although a civilian was killed and the minister's two bodyguards wounded.
Ten roadside bombs were defused near a bridge in Latifiyah, about 30km south of Baghdad, that police believed were set to target Shia visitors heading to Karbala, Babil police said.
Police also found the bodies of another four Shia pilgrims who had been shot repeatedly and dumped on Baghdad's northern outskirts.
On Thursday imams will read out the story of the suffering of Hussein and his followers and his eventual martyrdom and plays will be performed portraying the events, often accompanied by mass weeping.