Bangkok, Thailand (CNN) -- The crew of a cargo plane seized in Bangkok with tons of weapons from North Korea will be held in Thailand for 12 days for investigations, authorities said Monday.
The plane, which was detained during a refueling stop Saturday, had five people onboard -- four from Kazakhstan and one from Belarus.
The suspects were denied bail when they appeared in Bangkok's criminal court Monday on charges of illegal arms possession.
Thai authorities said the cargo aircraft contained about 35 tons of weapons, including rocket-propelled grenades, shoulder-launched rockets and tubes that may be missile components.
The pilot told authorities the aircraft was headed to Sri Lanka, but its final destination was unknown, said Panitan Wattanayagorn, a spokesman for the Thai prime minister.
Thai officials acted after working with several intelligence agencies for several weeks, the spokesman said. The cargo was taken to a military base while the plane, which is registered in Georgia, remains in Bangkok.
The Sri Lankan Ministry of Defence said there were no shipments scheduled in the country either by air or sea from North Korea. Such an aircraft could not have landed in any of Sri Lanka's airports without prior authorization, officials in Colombo said.
The five face up to 10 years in prison if found guilty.
CNN's Dan Rivers and journalist Iqbal Athas contributed to this report.