PATNA (AFP) - At least 11 Indian policemen were killed in a landmine attack staged by suspected Maoist guerrillas on Tuesday in the eastern Indian state of Jharkhand, police said. The ambush marked the latest violence in an escalating fight between security forces and the ultra-leftist rebels, who are entrenched deep in jungles across a swathe of eastern and northern India. "Eleven policemen were killed after Maoists targeted them when they were returning in vehicles after completing patrolling duty," senior police officer R.K. Malik told AFP. Around a dozen security personnel were injured in a firefight that erupted after the landmine ambush, Malik said by telephone from the state capital of Ranchi. The attack occurred in the village Dhardhariya in Loharadaga district, he added. Lohardaga is a hotbeds of the outlawed Maoist guerrillas in the mineral-rich Jharkhand state. In January, Jharkhand police shot dead nine suspected Maoist guerrillas in the state's Latehar district. The Maoist movement, which began in 1967, feeds off land disputes, police brutality and corruption, and is strongest in the poorest and most deprived areas of India, many of which are rich in natural resources. Some 171 suspected lef-twing guerrillas were killed last year along with 713 civilians in Maoist-linked violence compared to the previous year's tally of 591. A total of 285 policemen also died in 2010. Premier Manmohan Singh has called the insurgency India's main internal security threat and has urged state governments to increase pro-poor welfare measures, especially in Maoist-hit regions, to help counter the ultra-leftists.