Attacks north of Baghdad, including a car bomb set off by a suicide attacker, killed six people on Friday, just days after Iraq's parliamentary election.

The bloodshed comes with officials counting votes from Wednesday's polls, the first since US troops withdrew in late 2011, amid a protracted surge in nationwide unrest that has left more than 3,000 dead already this year.

Iraqi authorities blame spillover from the civil war in neighbouring Syria and say the powerful Islamic State of Iraq and the Levant (ISIL) jihadist group is behind most of the violence.

But critics say the government should do more to reach out to disaffected Sunnis to undermine support for militancy.

In Friday's deadliest attack, a suicide bomber set off a vehicle rigged with explosives on a highway connecting Baghdad to the town of Dujail, in Salaheddin province, killing four soldiers and wounding two others, officials said.

The blast came a day before Shiite pilgrims head through the predominantly-Sunni town on their way to Samarra, site of a major shrine, to commemorate the death of a venerated figure in Shiite Islam.

Sunni militant groups, including ISIL, frequently target Iraq's Shiite majority, whom they regard as apostates, particularly during annual commemoration rituals.

Elsewhere on Friday, gunmen killed two members of the Yazidi sect in the town of Rabiyah, near Iraq's border with Syria in northern Nineveh province, according to security and medical sources.

The attacks are the latest in the country's worst bloodshed since it emerged from a brutal Sunni-Shiite sectarian war that claimed tens of thousands of lives in 2006 and 2007.

Prime Minister Nuri al-Maliki, who is bidding for a third term in power, has been blamed by critics for the deterioration in security, as well as rampant corruption and allegedly insufficient improvement in basic services.