Maoist rebels killed 75 policemen in a jungle ambush in central India on Tuesday in the worst ever massacre of security forces by the left-wing extremists, officials said. A patrol from the Central Reserve Police Force (CRPF) was attacked at dawn in the state of Chhattisgarh and when reinforcements rushed to the scene they were surrounded by hundreds of heavily-armed rebels. In a hail of automatic gunfire and landmine explosions, 75 officers were killed, seven were injured and a heavily armoured anti-mine vehicle sent to retrieve the wounded was blown up, government officials and police told a foreign news agency. Home Minister P. Chidambaram expressed shock at the bloodbath and said the men had "walked into a trap." "This shows the savage nature of the Maoists -- the brutality and savagery which they are capable of," Chidambaram told reporters in New Delhi.