Baghdad  - At least 9 people were killed and 40 others wounded when a car bomb ripped through a bus station in the district of Balad in Saladdin province, a police source said on Saturday.

The victims were believed to have been heading to the holy city of Karbala to mark the al-Ziyara al-Shaabaniya or the mid of Shaaban visit pilgrimage on Sunday.

"An explosive vehicle in central Balad went off last night, killing nine civilians and injuring 40 others," the source, who spoke on condition of anonymity for safety reasons, told Voices of Iraq (VOI).

"The blast also left material damage to a number of nearby parked vehicles," the source added. Balad is some 90 kilometres north of Baghdad.

In Karbala, security measures were tightened in preparation for the occasion in which millions of pilgrims from Iraq and neighbouring countries are expected to pour into the city 110 kilometres south- west of Baghdad to commemorate the birth of the 12th Imam revered by Shiites.

A total ban on the movement of cars has been in effect since Friday, security officials said. A total of 40,000 security personnel will be deployed.

The Iraqi Air Force will carry out reconnaissance flights over all areas before and during the pilgrimage, while the US Air force will secure the area around the city. Hundreds of policewomen to search and deal with female pilgrims have been deployed to all checkpoints inside and outside of the city.

Shiite pilgrims have been a constant target of extremist Sunni Muslim groups operating in Iraq, mainly al-Qaeda, during their annual religious celebrations.

US and Iraqi authorities say al-Qaeda militants have increasingly been relying on women to conduct suicide bomb attacks, as their clothing makes it easier for them to evade security searches.

On Thursday, two women suicide bombers wearing explosive belts blew themselves up amid pilgrims in the Iskandariyah district 40 kilometres south of Baghdad as they were on their way to the holy city. At least 20 people were killed and around 100 injured. (dpa)