A series of attacks killed five people in northern Iraq on Wednesday, all of them in a swathe of disputed territory where diplomats fear tensions could spill over into all-out armed conflict.

The violence struck in and around the ethnically mixed cities of Kirkuk and Tuz Khurmatu, which lie at the centre of a tract of land stretching from Iraq's eastern border with Iran to its western frontier with Syria.

Kurdistan wants to incorporate the area into its three-province autonomous region over the objections of the central government in Baghdad.

Near Kirkuk, a roadside bomb killed three people -- a man and two women, all of whom were relatives -- as they were driving a truck filled with produce, police and a doctor said.

In the city itself, gunmen killed a soldier and wounded another, while a tribal chief was found dead in Tuz Khurmatu, having suffered multiple gunshot wounds. His body also bore signs of torture, officials and medics said.

The unresolved row over the tract of territory is persistently cited by diplomats and analysts as one of the biggest threats to Iraq's long-term stability, with fears the tensions could result in armed conflict between the central government and Kurdish security forces.

Iraq has seen increased levels of violence since the beginning of the year, coinciding with protests by the country's Sunni Arab minority, which alleges it is being unfairly targeted by the Shiite-led authorities.