Five people were killed when their car was hit by a roadside bomb outside the local offices of one of Iraq's main Sunni Arab political parties on Saturday, police said.

Another two were wounded in the blast close to the Iraqi Islamic Party headquarters in Khalis, a violent town roughly 60 km north of Baghdad.

Police said the attack appeared to target members of the party, which is the mainstay of a Sunni coalition that took part in this month's parliamentary election.

Insurgent groups such as al Qaeda in Iraq have called the election a farce and threatened attacks against Sunni politicians who took part.

The mixed Sunni and Shi'ite area in the west of Diyala province has seen heightened levels of violence in recent months, much of it claimed by al Qaeda and similar groups.