BANGKOK: A Thai court ordered an extended 12-day detention Monday for the crew of a cargo plane loaded with North Korean weapons, as Thailand said it was trying to determine if the aircraft's destination was in Asia or the Middle East.

The Bangkok Criminal Court accepted a police request to hold the five-man crew in prison pending further investigations in a case that could shed new light on the illicit weapons trade from North Korea, which is widely accused of selling weapons to nations in Africa and the Middle East, in violation of U.N. sanctions.

The United States, which is particularly concerned about North Korea selling weapons and nuclear technology in the Middle East, reportedly tipped off Thai authorities to the aircraft's illicit cargo, according to Thai media reports that the government and U.S. Embassy declined to comment on.

Thai officials impounded the Ilyushin IL-76 transport plane Saturday and discovered 35 tons of explosives, rocket-propelled grenades and components for surface-to-air missiles.

Members of the crew — four from Kazakhstan and one from Belarus — were charged Sunday with illegal arms possession, which carries a penalty of up to 10 years in prison. The court on Monday approved an initial request for a 12-day extension, which can be extended up to 84 days, said police spokesman Pongsapat Pongjaren.

Thailand convened an emergency session of its National Security Council, after which officials ruled out any threat to Thailand's security and said the investigation would be carried out carefully, slowly and in close cooperation with the United Nations.

The council's Secretary-General Thawil Pilansri said military experts were analyzing the weapons at a base in the nearby province of Nakhon Sawan, where they were moved by trucks Saturday night under high security.

"After an initial inspection we did not find any nuclear-type weapons," said Air Vice Marshal Metha Sungkawijit, in response to a reporter's question.

Government spokesman Panitan Wattanayagorn said the aircraft was headed for the Sri Lankan capital Colombo but authorities were investigating if the flight plan was misleading and the final destination was in the Middle East, noting the aircraft had recently stopped in the United Arab Emirates.

"We believe after Colombo there may have been another destination," he said.

On Wednesday the plane was flown from the United Arab Emirates to Bangkok where it landed without any cargo for a refueling stop and continued on to Pyongyang. It left the North Korean capital on Friday and returned to Bangkok for a scheduled refueling before it was due to fly to Sri Lanka, Panitan said.

"We had information that the plane was carrying weapons, and so we sent officers to search," Panitan said, declining to confirm Thai newspaper reports that the tip came from American authorities.

U.S. Embassy spokesman Michael Turner said the embassy could not confirm or deny any U.S. role.

The latest U.N. sanctions — which ban North Korea from exporting all arms or weapons — were imposed in June after the reclusive communist regime conducted a nuclear test and test-fired missiles. The sanctions were aimed at derailing North Korea's nuclear weapons program, but also banned the North's sale of any conventional arms.

The seizure came just days after President Barack Obama's special envoy made a rare three-day trip to North Korea on a mission to persuade Pyongyang to rejoin six-nation nuclear disarmament talks. Envoy Stephen Bosworth said the two sides had reached an understanding on the need to restart the talks.

Arms sales are a key source of hard currency for the impoverished North. Pyongyang is believed to earn hundreds of millions of dollars every year by selling missiles, missile parts and other weapons to countries like Iran, Syria and Myanmar.

The crew members insist they thought they were carrying oil-drilling equipment and were not aware of any illicit cargo, said defense lawyer Somsak Saithong.

"They didn't know what was in the boxes, they were just transporting them," the lawyer told reporters. "Their job is to pick up the cargo and go to the destination."

Later in the day, the court rejected their request for bail, he said.

The flight plan turned over to Thai police says the plane was registered to Air West, a cargo transport company in the former Soviet republic of Georgia and was carrying oil-drilling equipment, said Somsak.

In August, the United Arab Emirates seized a Bahamas-flagged cargo ship bound for Iran with a cache of banned rocket-propelled grenades and other arms from North Korea, the first seizure since sanctions against North Korea were ramped up.

In July, a North Korean ship believed to be bound for Myanmar and carrying suspicious cargo, possibly illicit weapons, changed course and headed home after it was monitored for more than a week by the U.S. Navy.