Security forces started combing the heavily forested mountain areas of northeastern India's troubled Manipur state yesterday, a day after 16 policemen were killed in a rebel ambush, an official said. Army, police and paramilitary soldiers were combing 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 any details about the kind of weapons found. The attack involved 40 to 50 heavily armed rebels, Parashar added.Sixty armed police officers who had been supervising elections in Bishenpur district were travelling in a six-vehicle convoy back to their district headquarters in Bishenpur town when rebels fired on them with automatic weapons on Saturday. Police retaliated and a fierce gunbattle ensued in which 14 policemen were killed on the spot and another eight were critically wounded, two of whom later succumbed to injuries in a hospital in Imphal.