CALCUTTA: Maoist rebels detonated land mines and set a security outpost ablaze in eastern India, killing at least 21 policemen in the worst-ever attack on police in the restive area.

An additional seven officers were wounded in the brazen assault Monday by more than 100 communist fighters, who also stole weapons from the security post in Shilda village of West Bengal state, said district magistrate N.S. Nigam.

"Never before the police here have suffered so many losses in one attack," Nigam told The Associated Press on Tuesday.

Shilda is about 105 miles (170 kilometers) southwest of state capital Calcutta.

Kishenji, a top Maoist leader in the area, claimed responsibility for the attack in a call to a local television station. He said it was in retaliation for a recent security crackdown against the rebels.

Police reinforcements scoured the area Tuesday for the assailants who fled after the assault, Nigam said.

Inspired by Chinese revolutionary leader Mao Zedong, the rebels have fought for more than four decades demanding land and jobs for farmers and the poor. The guerrillas are active in 20 Indian states.

In the past few months, the Indian government has cracked down on the outlawed rebels saying it was ready to discuss all their demands, but only if they gave up violence.

About 2,000 people — including police, militants and civilians — have been killed in violence over the past few years. The rebels are also known as Naxals or Naxalites, after Naxalbari, the village in West Bengal state where their movement was born in 1967.