The crew of the aircraft held in Bangkok after it was found to be carrying a large stock of war weapons say they planned to offload part of their cargo in Sri Lanka and the Middle East, investigators say.
A police source said some of the suspects admitted after more than six hours of questioning that they planned to unload part of "the goods" on their way back to Ukraine.
But they refused to name the buyers or locations, the source said.
The source, who is involved in the investigation, said the five crew members of the aircraft carrying the 35 tonnes of weapons from North Korea denied any involvement in arms trafficking.
The suspects said they were aircraft crew and had no knowledge the "goods" they transported were war weapons. They said they initially thought the cargo was oil pipes used as part of oil rigs, the source said.
The source said Mikhail Petukhou, the aircraft pilot, told investigators through an interpreter the plane travelled from Ukraine.
It made two stops for refuelling, at Azerbaijan and the United Arab Emirates, before heading to the North Korean capital of Pyongyang to load the cargo.
The plane then landed at Don Mueang for refuelling and planned to stop at Sri Lanka for more fuel before flying the cargo back to the Ukraine, the source said.
Thai security authorities seized the weapons on Saturday from the plane travelling from North Korea.
Authorities searched the aircraft after being tipped off by their US counterparts.
Five foreigners on board the aircraft were detained, the weapons confiscated and the plane impounded.
Four of the suspects hold Kazakh passports and the other a Belarus passport. Besides the pilot Mr Petukhou, 54, who is from Belarus, the other four crew were identified as Alexandr Zrybnev, 53; Viktor Abdullayev, 58; Vitaliy Shumkov, 54; and Ilyas Issakov, 53, from Kazakhstan.
The source said at this stage the suspects could only be charged with possession of weapons and ammunition without a licence.
Acting government spokesman Panitan Wattanayagorn said the weapons include missiles, explosives and tubes.
Officials from the Kazhakstan embassy in Bangkok and a Russian interpreter were called in yesterday to take part in the questioning of the suspects at the Crime Suppression Division.
The five suspects will be taken to the Criminal Court on Ratchadaphisek Road today for further detention.
Prime Minister Abhisit Vejjajiva said the government would stand by domestic laws as well as comply with UN resolutions in approaching the issue.
He said investigators had made good progress in their investigation and charges were expected to be brought soon.
Authorities will further examine the details of the weapons, the prime minister said.
Mr Abhisit said while the investigation was under way, the government was obliged to inform Kazhakstan and Belarus of the detention of their nationals.
The countries where the aircraft was registered and where the weapons originated would also be informed.
Mr Abhisit said the "goods" confiscated were made by a Korean-owned company and the aircraft was registered in Georgia.
At present, the weapons and the aircraft are being held at the air force's arms depot in Wing 4 in Nakhon Sawan's Takhli district.
The prime minister said at this stage it was not clear what the weapons were intended for.
He said the seizure of the weapons was a collaboration between Thai intelligence agencies and its foreign counterparts.
Bangkok Post