The blast in a forest area of Bihar state came following a lull in attacks on policemen since six officers were shot in May in an ambush in Chhattisgarh state.

"Four CRPF (Central Reserve Police Force) were killed when their vehicle was blasted by an IED (improvised explosive device) set by Maoists in a forested part of Gaya district," senior officer M.K. Sinha told AFP by telephone.

Sinha said that three men died on the spot and one later succumbed to his injuries.

"Four who were seriously injured are now being taken to hospital in Patna city and two others with minor injuries were admitted to a local hospital," he said.