Thailand will press charges against the crew of a plane forced to land in Bangkok and found to be carrying arms from North Korea.
It says it is unclear where the plane was going.
Thai police arrested five people and seized tonnes of weapons from a cargo plane that flew into Don Mueang airport from Pyongyang on Friday.
Military and police sources said the United States had tipped off the Thai authorities about the 35 tonnes of arms, which flouted United Nations sanctions against North Korea.
They said the five crew members - four from Kazakhstan and one from Belarus - were saying little.
He said the authorities believed the plane had initially planned to refuel in Sri Lanka and it was not clear why the crew had asked to make an emergency landing in Bangkok to refuel and check the wheel.
The authorities have declined to give details about the arms.
A military source said the haul included rocket-propelled grenades, missile and rocket launchers, missile tubes, surface-to-air missile launchers, spare parts and other heavy weapons.
Experts will be taking a closer look on Tuesday.
The plane was an Ilyushin IL-76 aircraft, registered in Georgia.
North Korea has been hit with fresh United Nations sanctions to punish it for a nuclear test in May.
These are aimed at cutting off its arms sales, a vital export item estimated to earn the destitute state more than $1 billion a year.