A car bomb killed two pilgrims Wednesday in Iraq on the eve of a major Shiite religious ceremony and the nephew of the parliament speaker died in a separate attack, officials said.

No group claimed responsibility for the bloodshed, but Sunni militants often target Shiite pilgrims in the run-up to major rituals and attack officials in a bid to destabilise the government.

The pilgrims were killed when a car bomb exploded as they were walking to the shrine city of Karbala to take part in Shiite Arbaeen ceremonies due to climax on Thursday, police and a doctor said. Eight other pilgrims were wounded.

Arbaeen marks 40 days after the Ashura anniversary commemorating the slaying of Imam Hussein, one of Shiite Islam's most revered figures, by the armies of the caliph Yazid in 680 AD.

In the northern city of Mosul, gunfire killed the nephew of Iraq's parliament speaker Osama al-Nujaifi, a Sunni politician, a police officer and a doctor said. The youth was the son of Nujaifi's brother and bodyguard Khaled.

The precise circumstances of the shooting were not immediately clear.

And a day earlier, gunmen shot dead three policemen in the town of Tarmiyah, north of Baghdad, officials said.

The violence came amid political tensions between Shiite Prime Minister Nuri al-Maliki and a secular-backed party in his fragile national unity government.

It also coincides with the blocking of a major highway by Sunni protesters who are demanding an end to anti-terror legislation they say is being misused by the Shiite-led government to target their minority.

Attacks in Iraq have dropped dramatically since their peak in 2006 and 2007 but the country remains locked in a "low-level war", the Iraq Body Count monitoring group said in a report published on Tuesday.