The Il-76 was unloaded by Thai soldiers
Thailand has seized a cargo plane refuelling in Bangkok airport, which it says was carrying weapons from North Korea to an unknown destination.
The five crew members were also detained.
Rocket-propelled grenades, missiles and other weapons were found aboard, military investigators said.
It is believed that the plane had made an emergency request to refuel. It had taken off from the North Korean capital Pyongyang, the Thai Air Force said.
According to local media reports, four members of the crew are from Kazakhstan, and one from Belarus.
Thai officials said they had acted on a tip-off from foreign intelligence, with one official telling Reuters news agency, on condition of anonymity, that the US had supplied the information.
"It [the plane] came from North Korea and was heading for somewhere in South Asia, probably Pakistan," the same official added.
Another unconfirmed report suggested Sri Lanka as the destination.
Local media say about 40 tons of weaponry were found aboard the chartered plane, a Soviet-designed Il-76.
The crew are said to have requested a translator from the Russian embassy
The reported items have been moved to a Thai military facility.
Thai Deputy Prime Minister Suthep Thaungsuban said the crew had declared the cargo as "oil drilling equipment", according to AFP news agency.
"But when we examined, we found it was all weaponry," Mr Suthep, who is also in charge of national security, told reporters.
"This case will proceed carefully as there are many parties involved... Everything must proceed transparently."
The UN recently increased sanctions against North Korea in a bid to cut off its arms sales as punishment for a nuclear test in May.
Arms sales are a vital export item estimated to earn the destitute state more than $1bn (£615m) a year, analysts say.
The North's biggest arm sales come from ballistic missiles, with Iran and other Middle Eastern states being customers, according to US government officials.