A bomb tore through an armour-plated car near a disputed town north of Baghdad on Tuesday, killing two election candidates and badly hurting a mayor, weeks before Iraq's first vote since 2010.

The blast in Tuz Khurmatu, in which a bodyguard also died and another was wounded, brings to 11 the number of candidates in the provincial council elections who have been killed.

Mayor Shallah Abdul, council chief Abdulqader Naimi and Salaheddin provincial councillor Rashid Khorshid had been travelling together to inspect a road paving project north of the town when the bomb went off near their car.

Naimi and Khorshid, both candidates in provincial elections due to be held on April 20, were killed, and Abdul was badly wounded and transported to a hospital in nearby Kirkuk city, capital of Kirkuk province that neighbours Salaheddin.

"What happened today is a terrorist operation," Kirkuk provincial governor Najim al-Din Omar Karim said. "They were targeting the democratic process, as we are close to elections."

Referring to a wide variety of political disputes in Iraq -- between Arabs and Kurds, and within the national unity government itself -- Karim added: "As long as the problems continue, the terrorist groups will reflect these differences by carrying out criminal activity."

A total of 11 election candidates have been killed, according to an AFP tally, and authorities have already postponed the polls in two large provinces, throwing into doubt the credibility of the vote, Iraq's first since parliamentary elections in March 2010.

The polls are seen as a key barometer of support for Prime Minister Nuri al-Maliki as he grapples with criticism from within his unity cabinet and months of ongoing protests in the minority Sunni Arab community.

The attack is likely to raise tensions in the town which is at the centre of a years-long row that politicians have warned threatens civil war.

Tuz Khurmatu, home to about 110,000 Arabs, Kurds and Shiite Turkmen, lies 175 kilometres (110 miles) north of Baghdad at the centre of a tract of disputed territory claimed by both the mostly-Arab government in Baghdad and the autonomous Kurdish region.

The dispute is often cited by officials and diplomats as the biggest long-term threat to Iraq's stability.

The establishment in September of the federal Tigris Operations Command, which covers disputed northern territory, drew an angry response from Kurdish leaders and increased tensions with the federal government.

Then on November 16, a firefight broke out during an attempt by Iraqi forces to arrest a Kurdish man in the town.

One person was killed and others were wounded, further worsening relations between Baghdad and Kurdistan as both sides deployed reinforcements.

The crisis has since eased, but the dispute over territory remains unresolved.

Violence elsewhere in Iraq on Tuesday left one person killed and 11 others wounded, officials said, as the country grapples with a spike in unrest 10 years since a US-led invasion ousted dictator Saddam Hussein.

A total of 230 people have been killed so far this month, according to an AFP tally, already more than in February.