Thai authorities will bring charges against five men from eastern Europe detained in Bangkok with a plane full of North Korean weapons, premier Abhisit Vejjajiva said on Sunday.
The cache, including missiles and rocket-propelled grenades, was discovered after the crew, four men from Kazakhstan and one from Belarus, landed for refuelling at Bangkok's Don Mueang airport on Friday, he said.
"We will strictly follow our own laws and UN resolutions. The investigation is progressing. Charges will soon be set," Abhisit told reporters.
But Thailand does not yet know where the weapons were bound, he said.
"We are not yet clear why they were transporting these weapons, we only know they were due to refuel in Sri Lanka," Abhisit told reporters.
"Security and intelligence services are continuing to investigate. It is not yet clear if this is terrorist activity," he said.
The plane began its journey in North Korea's capital Pyongyang. Abhisit confirmed that the weapons came from a North Korean company and the plane was registered in Georgia.
Thai media reported it was a Russian-made plane carrying 40 tonnes of weaponry, which police commander Lieutenant General Thangai Prasajaksattru said included "rocket-propelled grenades, missiles and other war weapons."
Abhisit said the crew requested permission to land for refuelling in Bangkok and then lied to inspectors about its cargo, saying it carried only oil drilling equipment.
"They committed two crimes, firstly they gave false information about their cargo, and secondly that cargo was found to be weapons," he said.
"The plane landed on Friday. We received the tip off from intelligence reports that said this plane was suspicious. When the plane refuelled, we searched it and found the weapons," he explained.
Officials previously said the plane had landed on Saturday morning.