NEW DELHI: India's Maoist rebels aim to overthrow the Indian state by 2050, a top government official was quoted Saturday as saying, warning security forces faced a "long, bloody war" to defeat the rebels.

The Maoists are taking a gradual approach to building their forces for a "final and lethal assault, aiming to overthrow the government by 2050 or 2060," said India's home secretary G.K. Pillai, citing documents seized in raids.

"We have a long, bloody war ahead," Pillai told a seminar on left-wing extremism Friday, according to television and newspaper reports.

His statements came as police in the eastern state of West Bengal sought the release of a teacher, abducted Friday, whom the Maoists have threatened to kill if authorities do not free six prisoners.

India's government, which sees the rebels as its biggest internal security threat, has launched offensives against Maoists in several areas but has failed to curb their operations significantly.

"It's quite likely violence will go up in 2010 or 2011," Pillai said.

"We don't have the forces to move into areas where they (Maoists) are positioned," said Pillai, adding at least 908 people died in Maoist attacks in 2009, the highest since 1971.

Security operations "have not hit even five percent of their hardcore militants," he said, adding the rebels were well-funded with a budget of about 14 billion rupees (308 billion dollars), obtained largely through extortion.

But the tide would turn in India's favour within three years "and it will probably take another seven to 10 years before we take complete control of civil administration" in areas where Maoists hold sway, Pillai forecast.

He called the rebels "highly motivated" and said they "operate like a well-trained army."

The insurgency began as a peasant uprising in 1967. The rebels are active in 20 out of 28 states with strongholds in a so-called "Red Corridor" stretching across north and eastern India.

The Maoists are using an administrative vacuum and under-development to establish their hold over large tracts of land across state boundaries.

In February, India gave a cautious response to a rebel offer of peace talks, saying the insurgents must first stop their attacks and make a formal proposal.