
Lt-General Camronwit Toopkrajank tried to board a flight to Thailand on Monday when a 22mm North American Arms pistol was found in his hand luggage.
The spokesman, who based his statement on a preliminary report, said the Japanese have charged Camronwit with trying to carry a weapon onto a plane. So, even if the gun was registered, it would not have made a difference.
He said Thai police would do everything they could to try to help Camronwit, who had travelled to Japan on June 18 to observe a waste incineration plant.
Prawut said the Japanese police had submitted the case to public prosecutors, who had not yet decided whether to make it a court matter.
Japan is entitled to detain Camronwit for no more than 20 days, the spokesman said, adding that he has not been allowed visitors.
Deputy Foreign Minister Don Pramudwinai said the Thai Embassy in Tokyo would assist Camronwit as best it could. It was too early to talk about Camronwit being extradited as the prosecutors are still investigating the case, Don said.
He said Tokyo took gun possession seriously as it considered it a national security matter.