It was the third attack in the city in the last two days as Shias observe the anniversary of Imam Mohammed al-Mehdi's birthday. — Photo by AP

BAGHDAD: A bomb attached to a policeman's car blew up on Saturday in the Iraqi city of Kerbala, killing at least three people and wounding 15 others during an annual Shia pilgrimage, officials said.

It was the third attack in the holy city in the last two days as Shias observe the anniversary of Imam Mohammed al-Mehdi's birthday, one of the annual pilgrimages that have evolved into shows of strength for Iraq's majority Shias since the fall of Sunni dictator Saddam Hussein in 2003.

The latest blast occurred near a security checkpoint in Kerbala, 80 kilometres southwest of Baghdad, and most of the casualties were police officers, police and provincial council officials said.

On Friday a car bomb exploded in a garage near a hospital west of Kerbala. Police said four people were killed and 20 wounded.

In a separate incident, a bomb placed under a parked car killed two people and wounded four others in northern Kerbala on Friday, according to an army commander, while a hospital source said the blast killed three people and wounded 23 others.

Shia religious rites were banned under Saddam. They have been targeted frequently by Sunni insurgents since the US-led invasion that deposed him.

Last year car bombs killed and wounded scores of people during the Imam Mehdi observance in Kerbala.

While violence has fallen sharply in Iraq in recent years, militants still launch hundreds of attacks each month.