Thai investigators said Tuesday they have found mass weapons including rocket-propelled grenades, components for surface-to-air missiles and other armaments seized from a plane setting off via North Korea.

The Russia-made Iiyushin II-76 transport plane was seized at Don Mueang airport on Saturday and discovered what they said was 35 tons of war weapons.

Thai government spokesman Panitan Wattanayagorn said the plane from Pyongyang stopped in Bangkok late Friday to refuel.

An air force official involved in the inspection said Thai authorities had been asked by the United States to investigate the plane and its cargo.

We were approached by the United States, seeking our cooperation to examine the suspected plane. It came from North Korea and was heading for somewhere in South Asia, probably Pakistan, he said.

Prime Minister Abhisit Vejjajiva said Interpol was also involved.

US Secretary of State Hillary Rodham Clinton praised the seizure, saying it shows that sanctions can prevent the proliferation of weapons and it shows that the international community when it stands together can make a very strong statement.

Thai police continue to hold the crew members -- four from Kazakhstan and one from Belarus -- who were charged with illegal arms possession.

They face up to 10 years in prison and have denied knowledge of the weapons, saying they thought they were ferrying oil-drilling equipment.

Impoverished North Korea is believed to earn hundreds of millions of dollars every year by selling missiles, missile parts and other weapons to countries such as Iran, Syria and Myanmar.

The United Nations Security Council approved rules in June that ban North Korea from exporting arms and called on states to inspect its cargoes in their airports and seaports if they are believed to carry banned items.