Mumbai: Maoist insurgents killed three policemen on Thursday in a remote part of western India, police said, marking the latest ambush by the rebels who have long been battling to overthrow the government.

The attack occurred in a hilly and undeveloped rebel stronghold in western Maharashtra state.

“A police party belonging to the special action group were attacked by Maoists in the Gadchiroli district,” Maharashtra’s director-general of police Sanjeev Dayal said. “Three policemen were killed.”

The police were on a combing operation in a forested area when the rebels triggered a landmine explosion and there was cross-firing, a senior officer at the Gadchiroli police control room said.

There are frequent outbreaks of violence in the so-called “Red Corridor” created by India’s Maoists, which stretches throughout central and eastern India.

The once-ragtag group of rebels has developed into a strong insurgent force, described by Prime Minister Manmohan Singh as the country’s most serious internal security threat.

In an unrelated incident, police killed one Maoist in a shootout in the same district on Thursday, Dayal said.

In May, a heavily armed gang of Maoists killed at least 23 people in central India, including top local politicians. In 2010, a rebel assault killed 76 police.

The Maoists have been fighting for decades in the forests and rural areas for what they say are the rights of tribal people and landless farmers.

They demand land and jobs for the poor, and want to establish a communist society by toppling what they call India’s “semi-colonial, semi-feudal” form of rule. The revolt is believed to have cost tens of thousands of lives.