T J Longkumer, the inspector general of police, estimated that 70 policemen were  missing. "We have not been able to establish contact," he told Reuters.

Rebel stronghold

The brazen ambush highlights the strong rebel presence in significant portions of India, especially in poor rural regions left out of India's economic boom.

in depth

  India's costly war against Maoists
  India's battle against the Maoists
  Q&A: The Maoists of India
  Indian villagers take on Maoists
  Timeline: Major Maoist attacks

In a separate attack in eastern Jharkhand state on Tuesday, rebels killed five people, police said. It was not immediately clear why the Maoists killed them.

Security forces launched a counter-offensive against Maoists earlier this year but recent attacks raise questions over how well prepared security forces are to tackle the insurgency.

In April, a similar ambush by Maoists killed 75 policemen and a month later a bus bombing killed 35 people, including security forces.

Both attacks occurred in the mineral-rich but largely poor Chhattisgarh state.

Rebels claim to be fighting for the right of poor peasants and landless workers and aim to topple the Indian state by 2050.

They operate from jungle bases and launch hit and run attacks on police, transportation networks and government buildings in east, central and southern India, where they control large territories.

Thousands have been killed since the insurgency started in the late 1960s and the Indian government has said that Maoist fighters represent the country's most dangerous internal security threat.