A suicide bombing in the Iraqi capital killed a police officer on Tuesday, while in the north of the country a gun attack on a car in Mosul left a husband and wife dead, security sources said.

The attack by gunmen in Mosul, 350 kilometres (217 miles) north of the capital, targeted a Christian man and wife in the west of the city, according to a police officer who requested anonymity.

In Baghdad, a suicide bomber blew up his car while passing a police patrol in the central business area of Saadun, an interior ministry official said.

The blast killed a police captain, and also wounded two other policemen and three civilians, the official said.

Violence in Iraq has declined significantly since its peak during the sectarian bloodbath of 2006 and 2007, but attacks remain frequent, killing 187 Iraqis in November, according to official statistics.

US troops are set to fully withdraw from the country by the end of the year, a move applauded by many Iraqis, but which has also raised concern about the capacity of Iraqi security services to protect the population.