BAGHDAD: A bomb planted on a parked motorcycle exploded today on the outskirts of the holy city of Karbala, killing at least 20 Shiite pilgrims and wounding more than 100 amid tight security for the huge religious procession, officials said.

The bomb exploded at about 11 am in an area known as Ibrahimia, near the east entrance - one of three - into Karbala, about 80 km south of Baghdad, said the official.

At least 108 people were wounded in the attack, the official said, adding that the area was clogged with pilgrims and the number of casualties could increase. A hospital official in Karbala confirmed the number of dead and wounded.

Hours earlier, two separate roadside bombs targeting Shiite pilgrims exploded in Baghdad, killing one and wounding seven others, a security official in the capital said. The official said the first attack took place at about 6:15 am in western Baghdad, killing one person and wounding three. He said a second explosion in southwest Baghdad wounded four pilgrims.

Karbala police spokesman, Maj Alaa Abbas, said more than 30,000 security personnel were deployed around the city. The measures included bomb-sniffing dogs at the three main entrances to Karbala and undercover intelligence agents in the crowds. But tight security in the past has failed to prevent bloodshed among Shiite pilgrims or at shrines.

During a Shiite pilgrimage in February 2009, a female suicide bomber attacked a tent filled with women and children resting during the walk to Karbala, killing 40 people and wounding 60 others. A month before that, a suicide bomber dressed in women’s clothing and hiding among Iranian pilgrims killed more than three dozen people outside a mosque in Baghdad’s Shiite neighbourhood of Kazimiyah. Earlier Wednesday, a senior security official said agents arrested 13 suspects believed involved in making explosive belts for suicide attacks.

The official said authorities believe the belts - including five seized by police - were intended for attacks on Shiite pilgrims.