Maoists rebels killed 13 policemen in a landmine attack in Jharkhand on Saturday, state TV said, prolonging what Prime Minister Manmohan Singh has described as the country's biggest internal security threat.

The rebels, who say they are fighting for the rights of landless labourers and poor farmers, have killed about 1,600 police and civilians in the last two years, the government has said.

Saturday's attack happened in the forests of Garhwa in Jharkhand.

Thirteen policemen were killed and two policemen were injured in the blast, Doordarshan, India's state TV Channel reported, citing state police officials.

India