TOKYO -- Police are investigating reports thatan explosion on board a Thai International Airways plane was caused by a grenade smuggled onto the aircraft as part of an underworld arms shipment, officials said Wednesday.
Earlier, National Police Agency officials had said they were checking a theory that Sunday night's blast was part of an insurance plot but denied reports that a bomb was involved.
Thai International's Flight 620, flying from Bangkok via Manila to the Japanese city of Osaka, suddenly lost cabin pressure and began a 25,000-foot nosedive.
Sixty-two of the 247 people aboard were injured, but the pilot regained control of the aircraft and landed it safely at its intended destination.
Police in Osaka said they were checking into television news reports that an unidentified passenger who belonged to Japan's largest gangster organization, Yamaguchi-gumi, smuggled a grenade on board and it exploded during the flight.
The reports said the grenade was probably part of an illegal arms shipment from Manila. Japanese underworld groups have been known to purchase arms in the Philippines and smuggle them into Japan.
'We're looking into all these theories,' the police spokesman said.
The public broadcasting system NHK quoted investigators as saying the blast probably was caused by a grenade detonated in a rear toilet. NHK said investigators were collecting metal fragments found in the plane following the explosion.
A National Police spokeswoman said authorities were questioning a passenger 'who appears to be a yakuza (gangster),' who was sitting near one of the rear toilets and was seriously injured when its walls collapsed as the plane lost pressure.
Thai International spokesman Masahiko Jomen and Ministry of Transport investigators refused comment on the reports.
In the Thai capital, the Bangkok Post published an interview with the plane's 48-year-old pilot, Amphol Ploymeekha, who said he had switched on the 'fasten seat belts sign' shortly before he heard an explosion from the passenger cabin during the flight.
Amphol said the European A-300 Airbus then strayed nearly 62 miles off course before plunging from 32,000 feet to 6,900 feet. He said 'there was nothing much' to bringing the plane under control.
'There is a flying procedure and all I did was follow it,' Amphol said.
The pilot, with 10,000 flying hours, said it was the second time he had flown the plane since it went into service Oct. 12, adding there were no previons indications of problems.