PANAMA CITY (AFP) - Panamanian authorities have released 32 of the 35 North Koreans detained since July after an undeclared cargo of Cuban arms was found on their ship, prosecutors said Thursday.

The remaining three North Koreans - the Chong Chon Gang vessel's captain, first officer and political secretary - face trial on arms trafficking charges, prosecutor Nathaniel Murgas told reporters.

He said the organized crime office ordered the sailors' release on Tuesday, and that they were turned over to immigration authorities.

The other crew members face up to 12 years in prison if convicted of arms smuggling.

The North Korean freighter was stopped on July 10 on suspicion of carrying drugs as it tried to enter the Panama Canal.

A search uncovered 25 containers of Cuban military hardware, including two Soviet-era MiG-21 aircraft, air defense systems, missiles and command and control vehicles.

Earlier this month, Panamanian officials said North Korea had agreed to pay a US$666,666 (S$ 850,525) fine for the release of the crew and ship.

The fine was imposed for endangering the waterway and providing "distorted information" about the "dangerous" cargo, the Panama Canal Authority (ACP) said.

But North Korea "has not yet paid us. The vessel remains held in canal waters," ACP administrator Jorge Quijano told AFP.

Julio Berrios, lawyer for the North Koreans, said that prosecutors had informed him "of nothing," and was unaware whether the fine had been paid or of the final whereabouts of his clients. It is not yet clear when the North Koreans will be repatriated.

"Administrative procedures are getting under way for the deportation of these citizens, although there's no definite date yet," National Immigration System spokesman Didacio Camargo said.

Both Havana and Pyongyang said the weapons aboard the freighter were obsolete Cuban arms being shipped to North Korea for refurbishment under a legitimate contract.

More than 200,000 sacks of sugar that concealed the weapons are held by the organized crime office, which is examining "several situations to verify their final destination," while the weapons are guarded by police pending a court decision, the prosecutor Mr Murgas said.

Chief prosecutor Ana Belfon said that "North Korea has not shown interest in its nationals. It was concerned about the fate of the sugar, but not the fate of its nationals." Panama's government has asked the United Nations to send a mission to determine whether the shipment violated the UN arms embargo against North Korea.

The UN has yet to make an official determination on the shipment.