RAIPUR, India - Maoists in India killed 75 policemen and injured seven in an ambush on Tuesday in the central state of Chhattisgarh, Home Secretary Gopal Pillai told AFP.

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, dozens of officers were killed and a heavily armoured anti-mine vehicle sent in to retrieve the wounded was blown up, a local government official and police sources told AFP.

The Maoists have stepped up attacks in response to a government offensive that began late last year to hunt them down in the forests of the so-called "Red Corridor" that stretches across north and eastern India.

Home Minister P. Chidambaram said the massacre showed the "savage nature" of the Maoists, who began their campaign for a Communist state in 1967 and are now active in 20 of India's 28 states.

"Something has gone very wrong. They seem to have walked into a trap set by the Naxals (Maoists) and casualties are quite high," he told reporters in New Delhi.

He had previously said he was ready for talks with the rebels on condition they renounced violence beforehand. Maoist leaders have said they will only talk once the offensive against them ends.

Chidambaram hardened his rhetoric at the weekend after 10 policemen were killed in a separate landmine attack in eastern Orissa state, calling the rebels "cowards".

On Monday, he said Naxalism, as the Maoist movement is known in India, was the "first enemy" of the country.

The chief minister of Chhattisgarh, Raman Kumar, told reporters in Raipur that the offensive against the Maoists, codenamed Operation Greenhunt, would continue in his state.

"We will have to be more cautious, but we will keep our operation on," he said.

In March 2007, the Maoists were blamed for an attack that also killed 55 policemen in Chhattisgarh.

In February, another 25 security forces were killed when Maoists riding motorbikes and in cars launched an attack on a police camp in eastern West Bengal state.

Assaults by the Maoists are an almost weekly occurrence in India, with security forces, schools, government offices, train tracks and police stations the usual targets.

Prime Minister Manmohan Singh has called the Maoists the biggest internal security threat to India.

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