Military investigators said that rocket-propelled grenades, missiles and other weapons were found on the plane.
The plan was refueling in Bangkok airport when it was seized by Thai authorities.
Local media reports that four members of the crew are from Kazakhstan and one from Belarus.
Thailand authorities were acting on a tip-off from foreign intelligence. One official, on condition of anonymity, stated that the US had supplied the information.
An official told Reuters
, "It [the plane] came from North Korea and was heading for somewhere in South Asia, probably Pakistan." An unconfirmed report suggested that Sri Lanka may have been the destination of the plane.
also reports that North Korea's biggest arm sales come from ballistic missiles, with Iran and other Middle Eastern states being customers, according to US government officials.
The weapons have been moved to a Thai military facility.