Baghdad, Jan 24 (Agencies): In the latest deadly attack on Shiites headed to mark religious rituals in a holy Iraqi city, a bomb explosion struck the crowd of Shiite pilgrims in Karbala killing six pilgrims on Monday, police and hospital officials said.

Authorities said 13 people were wounded in the morning blast in a parking lot where the car exploded near busloads of pilgrims on the outskirts of Karbala, a city 90 km south of Baghdad.

A second bomb was discovered nearby and dismantled before it could explode, police said.

Monday's attack followed a triple suicide bombing last week along two highways leading to Karbala that killed 56 and wounded at least 180, most of them Shiite pilgrims.

Hundreds of thousands of pilgrims are expected to gather in Karbala on Monday night to mark the end of Arbaeen, a 40-day mourning period to observe the 7th century death of the Imam Hussein, one of the Shiite sect's most revered figures.

No group so far has claimed responsibility for last Thursday's bombing, but suicide attacks are the trademark of the Islamic State of Iraq, an al-Qaida front group believed made up mostly of Sunni religious extremists.

Since the end of Saddam's rule, Shiite politicians have encouraged huge turnouts at religious rituals, which were banned under the former regime, as a demonstration of Shiite power.

Also on Monday, police said two bombs in Baghdad killed an Iraqi Army intelligence officer and his driver and wounded eight bystanders in separate strikes that hit a Shiite and a Sunni neighborhood. Hospital officials in Baghdad confirmed the fatalities.