Security forces searched the heavily forested mountain areas of northeastern India's troubled Manipur state Sunday, a day after 16 policemen were killed in a rebel ambush, an official said.

Army, police and paramilitary soldiers are searching the area where the attack took place and have recovered a cache of weapons, the state's police chief A.K. Parashar said. He did not give details about the kind of weapons found.

The attack involved 40 to 50 heavily armed rebels, Parashar added.

Sixty armed police officers who had supervised elections in Bishenpur district were traveling in a convoy of six vehicles back to their district headquarters in Bishenpur town when rebels fired on them with automatic weapons on Saturday.

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Police retaliated and a fierce gunbattle ensued. Sixteen police were killed and another eight were critically wounded.

It was the worst violence since the election began on Feb. 8. Voting is staggered in the insurgency-wracked region to help security forces prevent rebel attacks.

Parashar said it was unclear which rebel group was behind the attack.

The National Socialist Council of Nagaland and Manipur People's Liberation Front are among several rebel groups that have been fighting for decades for independent homelands in Manipur and the neighboring state of Nagaland.

The militants say the central government in New Delhi — 1,000 miles to the west — exploits the northeast's rich natural resources while doing little for the indigenous people, most of them ethnically closer to Burma and China than to the rest of India.

The northeast has poor infrastructure, widespread unemployment and a bitterness toward the national government that has nurtured dozens of militant groups.

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