Japanese police raided the offices of Yamaha Motor today after the government filed a criminal complaint against the company over its sale to China of small helicopters that officials said could have military uses.
Japan has repeatedly expressed concern about China's military buildup and urged Beijing to be more transparent about its motives.
The Ministry of Economy, Trade and Industry (METI) said it has been investigating Yamaha on suspicion that it had exported and tried to export small, unmanned crop-spraying machines without the required government permission.
"Yamaha did not get the necessary permission when they exported or tried to export its RMAX Type IIG helicopters," a ministry official said.
Chief Cabinet Secretary Shinzo Abe linked the investigation to efforts to halt the spread of weapons of mass destruction.
A Yamaha Motor spokesman, confirming that police and customs officials had raided the company on Monday morning, said ministry officials had searched its headquarters last December. The company denied any wrongdoing.
Yamaha, the world's second-biggest motorcycle maker after Honda Motor, has exported nine of the crop-spraying machines to China since August 2002, the company official said.
A Japanese newspaper report claimed that the Chinese company that Yamaha was dealing with was suspected of having connections to the People's Liberation Army.