Attacks in Sunni-majority areas of Iraq killed nine people Sunday, exactly a month ahead of parliamentary polls that remain in disarray after the mass resignations of election commissioners last week.

The violence came hours after seven soldiers were shot dead at a checkpoint in a late-night attack by militants in the north, the latest in a months-long surge in bloodshed that has killed nearly 500 people so far this month.

The unrest has been driven principally by anger in the Sunni Arab minority over alleged mistreatment at the hands of the Shiite-led authorities, as well as by the civil war raging in neighbouring Syria.

A suicide bomber detonated a vehicle packed with explosives on a major bridge in Ramadi, a city west of Baghdad where security forces are still grappling to retain full control after militants took over several neighbourhoods two months ago.

The blast killed seven people and wounded 10 more, and also badly damaged the Hauz Bridge, a key crossing used by civilians connecting the north and south of the city.

Ramadi originally had five bridges across the Euphrates River before a militant surge earlier this year.

But two are used exclusively by security forces, and two others -- including the Hauz Bridge -- have now been damaged to the point they can no longer be used.

Civilians in Ramadi are now able to use only the Albu Faraj bridge in the north of the city.

Ramadi is the capital of Anbar province, a predominantly Sunni desert region in west Iraq that shares a border with Syria.

In early January, anti-government fighters seized control of parts of the city and all of nearby Fallujah, also in Anbar.

But while security forces have managed to take back most of Ramadi, a stalemate persists in Fallujah, which remains in militant control.

Elsewhere on Sunday, two police officers were killed by a roadside bomb that exploded near their car in Tikrit north of Baghdad. Like Ramadi, Tikrit's population is made up mostly of Sunni Arabs.

- Seven soldiers killed -

The attacks came just hours after militants opened fire on an army checkpoint near the restive northern city of Mosul, killing seven soldiers in a late-night shooting.

In Mosul city itself, gunmen also killed a doctor.

Violence has surged in Iraq in the past year, with nearly 500 people killed so far this month, and upwards of 2,200 this year, according to an AFP tally.

Analysts and diplomats have urged the Shiite-led authorities to do more to reach out to the Sunni community to undermine support for militancy, but with the elections looming on April 30, Prime Minister Nuri al-Maliki and other Shiite leaders have taken a hard line.

The polls, however, have been thrown into disarray by the mass resignation last week of Iraq's nine election commissioners, citing parliamentary and judicial interference.

Though lawmakers say their resignations are unlikely to be accepted, and the commissioners have not left their posts, the sudden decision has raised the possibility of Iraq's first elections since 2010 being delayed.

"If IHEC stays this way, that means... the election will be delayed," Maliki warned last week, referring to the Independent High Electoral Commission.

"We will enter a tunnel we might not be able to get out of," the premier said. "Troubles will come, one after another, against the state."

The IHEC board has been frustrated with what it says is a vague provision in the electoral law that requires parliamentary hopefuls to be "of good reputation".

Based on that article, a judicial panel has barred several prospective lawmakers, including Maliki opponents such as former finance minister Rafa al-Essawi, with no obvious avenue of appeal.

Parliament has meanwhile reportedly ruled that the IHEC must not bar any candidates unless they have criminal convictions, a decision an electoral official said was at odds with that of the judicial panel.