Malaysian forces launched air strikes and mortar attacks against nearly 200 Filipinos occupying a coastal village today.
The assault follows firefights over the past week that killed eight Malaysian police officers and 19 Filipino gunmen in Borneo's eastern Sabah state.
National police chief Ismail Omar said ground forces that moved in after the airstrikes had encountered resistance from gunmen firing at them.
Police were combing an area of about 1.5 square miles to look for the Filipinos, he said.
The clansmen, armed with rifles and grenade launchers, had refused to leave the area, staking a long-dormant claim to the Malaysian state of Sabah, which they insisted was their sultan's ancestral birthright.
Foreign Minister Alistair Burt's admission that the Cameron government has "supported" a survey of attitudes to US drone strikes in Pakistan's tribal areas amounts to a tacit admission of British involvement.