BAGHDAD -- A 9-year-old schoolboy was among at least 12 people that insurgents killed across Iraq on Wednesday, rattling nerves ahead of a holiday weekend.

Violence has declined since the height of Iraq's insurgency, but the attacks once again showed that Sunni extremists seeking to undermine the Shiite-led government remain a lethal challenge to Iraq's security.

The child, Ahmed al-Obeidi, was killed when a parked motorcycle packed with explosives went off near a local politician's passing convoy in the northern oil-rich city of Kirkuk, according to police and a provincial council official. The boy and his brother were on their way to buy clothes for the holiday of Eid al-Adha, which begins later this week.

Four other people were wounded in the attack. Politician Ali al-Hashemi, an ethnic Turkomen and the apparent target of the blast, escaped unharmed.

Kirkuk, about 290 kilometres (180 miles) north of Baghdad, is home to mix of Arabs, Kurds and Turkomen, all competing to control the city.

Authorities typically tighten security ahead of holidays, seeking to thwart attackers who take advantage of times when employees are off work and families gather in public places such as parks and restaurants. A wave of attacks shortly before another Muslim holiday in August, Eid al-Fitr, killed more than 90 people in one of the deadliest days in Iraq this year.

Members of the security forces -- favourite targets for insurgents -- were also among those killed Wednesday, according to police.

In Baghdad's western Mansour neighbourhood, militants in a speeding car killed two soldiers at an Iraqi army checkpoint. A roadside bomb exploded shortly afterward as police headed to the scene, killing one policeman and wounding six people.

Shortly before dawn, a sniper shot and killed a police officer in the capital's eastern Mashtal neighbourhood.

In the afternoon, gunmen ambushed a minibus carrying employees of a state-run car parts manufacturer in Mishada, north of Baghdad, killing four people and wounding two. Two other people were killed when gunmen sprayed their car with bullets near Baqouba, in central Iraq.

In Tuz Khormato, some 210 kilometres (130 miles) northeast of Baghdad, a roadside bomb struck a police patrol, killing a policeman and wounding three others.

Health officials confirmed the casualty figures. All officials spoke on condition of anonymity because they were not authorized to release the information to reporters.

Also Wednesday, Supreme Judicial Council spokesman Abdul-Sattar Bayrkdar said authorities have begun summoning employees of the central bank to give testimony as part of a probe into alleged financial wrongdoing. None has faced arrest.

The questioning follows the issuing of arrest warrants for 16 bank officials, including longtime governor Sinan al-Shabibi, a politically independent economist who has led the institution since 2003. The investigation, launched by a special parliamentary committee, has raised concerns of political interference in the bank.

On remarks posted on his official website Wednesday, Iraqi Prime Minister Nouri al-Maliki denied that his administration was behind the investigation that led to the arrest warrants, seeking to quell allegations that the case is politically motivated.