NEW DELHI (Reuters) - Maoist guerrillas ambushed a paramilitary patrol in eastern India on Monday, killing 13 policemen in the biggest rebel attack this year, a state police officer said.

The attack took place in remote Sukma district, in the jungle of Chhattisgarh state, where members of the Central Reserve Police Force had been sent to flush the rebels out of their base.

The Maoists seek the overthrow of the Indian state and have operated for decades across a wide swathe of central and eastern India. They have grown in strength in recent times in areas where poor, tribal villagers have come into conflict with mining companies seeking resources for industrialisation.

Security experts say the insurgency is India's biggest internal security challenge.