RAIPUR (AFP) - Suspected Maoist guerrillas have killed at least seven Indian policemen in a landmine attack in the central Indian state of Chhattisgarh, police said Wednesday. The attack was the latest 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. "Seven policemen were killed on Tuesday night. The Maoists targeted them when they were returning in vehicles after completing patrolling duty," said senior police officer Ramniwas, who goes by one name. The attack occurred in Sukma town in Dantewada district, a hotbed of Maoist activity 515 kilometres (320 miles) south of state capital Raipur. 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. PM Singh has called the insurgency India's main internal security threat and has urged state govts to increase welfare measures, especially in Maoist-hit regions, to help counter the ultra-leftists. Some 171 suspected left-wing 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.