A suicide bomb and gun attack on a courthouse in the west Afghan city of Farah has left at least six people dead and 70 injured, most of them civilians.

Militants disguised as soldiers tried unsuccessfully to free suspected Taliban members, officials say.

After a fierce initial gun battle, shooting continued as militants took cover in at least one building.

Taliban insurgents said they were behind the attack in the strategic province, which borders Iran.

A bomb and gun attack on the governor's compound last May left six policemen, a civilian and four attackers dead.