A car bomb went off Sunday near the governor's residence in the turbulent northern city of Mosul, killing a policeman and wounding three civilians, hours after a lone gunman shot dead a prison officer in the city center, according to police officials.

It was not immediately clear whether Atheel al-Nujeifi, governor of Ninevah province, was the target of the bomb.

He was not at his residence in the BDawasa neighborhood at the time of the blast, said the officials, who spoke on condition of anonymity because they were not authorized to share the information with the media.

The bomb was in a car parked about 100 yards (meters) away from his home, suggesting it was meant to be detonated when the governor's convoy drove past, a tactic widely used by Iraqi insurgents.

The officials said a policeman was killed in the blast and three civilians were wounded.

Earlier Sunday, a gunman killed an off-duty prison officer in Mosul, 225 miles (360 kilometers) northwest of Baghdad. A police statement said the victim was a 1st lieutenant in his 20s who served at Badoosh prison on the city's outskirts. The gunman got out of a car, opened fire on the officer and then fled, it said.

The statement from the provincial police command did not give a motive for the shooting.

The car bomb and the shooting underline the precarious security situation in Mosul, which has yet to witness the dramatic reduction in violence seen in most other parts of the country.

The surprise victory by a local party led by the Sunni Arab al-Nujeifi in January's provincial elections added to tensions in Ninevah, where Mosul is the capital. His calls for an end to what he sees as Kurdish interference in the province has stoked tension between the province's Arab majority and its large Kurdish minority.

The party — the National Hedba Gathering — was formed in 2006 with the avowed goal of ending the rule of Kurdish parties, which dominated the previous provincial council because Sunni Arabs boycotted the last regional balloting in 2005.

Some 2,000 Kurds, meanwhile, staged a demonstration in Sheekhan, an area about 30 miles (50 kilometers) east of Mosul, to demand its annexation to the self-ruled Kurdish region. Sheekhan has a Kurdish majority.

In Baghdad, a bomb hidden in a plastic bag exploded Sunday night near a small cafe in a Shiite area of Dora neighborhood, killing four people and wounding 12, a police officer said. He spoke on condition of anonymity because he was not supposed to release the information.

Also Sunday, Iraq's trade minister, Abed Falah al-Sudani, appeared before parliament to answer allegations of corruption against several senior ministry officials and two of his brothers who serve as security guards.

The chairman of the parliamentary integrity committee, Sabah al-Saedi, alleged the minister's two brothers received at least $40 million in kickbacks on imports.

The former inspector general of the ministry, Abdul-Hadi Abdul-Muniem Hassan, told the integrity committee that one of the minister's brothers, Sabah al-Sudani, threatened to kill him and his family if he didn't keep silent about corruption.

Sabah al-Sudani was arrested last week in southern Iraq carrying large amounts of cash and two passports, in what the government said was an attempt to flee the country. The other brother, Majid, remains at large.

Al-Saedi said he would collect enough signatures of parliament members to dismiss the minister.

"I don't claim there was no failure," the minister said during the session. "But I call on the lawmakers to specify these failures to solve them and avoid things like this in the future."