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.[break]
The Maoists have been fighting a deadly low-intensity war against authorities for decades for what they say are the rights of tribal people and landless farmers.
"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.
The insurgency, which began in 1967, feeds off land disputes, police brutality and corruption, and is strongest in the poorest and most deprived areas of India, many of which are rich in natural resources.
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