RANCHI (AFP) - Twelve policemen were killed in a landmine blast triggered by suspected Maoist rebels Saturday in eastern India, a police spokesman said. The victims were on their way back after a routine patrol when the mine, planted near Puridih Dam, 240 kilometres from Jharkhand state capital Ranchi, exploded killing most of them on the spot, police spokesman SN Pradhan said. "All the personnel belonged to Jharkhand Armed Police," Pradhan said. Jharkhand is a known hotbed of the Maoist insurgency which grew out of a peasant uprising in 1967. The leftwing guerrillas are active in over half of India's 29 states and the rebels use a heavily forested region in the neighbouring state of Chhattisgarh as their headquarters. PM Manmohan Singh has described the Maoists as the biggest threat to India's internal security. The Maoists often target the overstretched and poorly trained security forces operating in the east of the country. The national government promised in July to create new, specialised commando units in the worst-hit Indian states of Chhattisgarh, Jharkhand, Andhra Pradesh and Orissa. It has also pledged to create six jungle warfare and counter-insurgency schools. In July, 21 commandos died when their patrol boat came under fire from Maoist rebels in the mineral-rich but impoverished Orissa state.