North Korea has insisted Cuban weapons found aboard a Pyongyang-flagged ship near the Panama Canal were part of a legitimate deal, and called for the release of the ship's crew.

Panama is to charge the crew of the Chong Chon Gang with crimes against internal security after detaining them on Tuesday, and has asked the United Nations to inspect the ship's cargo to determine if it breaches arms sanctions imposed on North Korea over its nuclear programme.

Pyongyang's foreign ministry on Wednesday said: "This cargo is nothing but ageing weapons which are to be sent back to Cuba after overhauling them according to a legitimate contract.

"The Panamanian authorities should let the crewmen and ship leave without delay."

The Chong Chon Gang was stopped near the Panama Canal on Tuesday, laden with a consignment of Cuban weapons and 10,000 tons of sugar. The weapons included disassembled rockets, Mig-21 aircraft parts and two anti-aircraft missile systems.

Sweetening the deal

Cuba admitted it was sending the weapons for repair to North Korea, but insisted they were "obsolete, defensive" Soviet-era arms and the deal was legitimate. The sugar was payment for the service, it added.

The crew rioted after being boarded, while the ship's captain was reported to have suffered a heart attack before trying to commit suicide.

North Korea countered that the captain and crew had been "rashly attacked", and condemned what it called a "violent action" by Panama.

Panama's prime minister, Ricardo Martinelli, said on Tuesday that the ship was violating United Nations resolutions against arms trafficking.

"The world needs to sit up and take note: you cannot go around shipping undeclared weapons of war through the Panama Canal," he said on a Panamanian radio station.

Likely violation

At the United Nations on Wednesday in New York, diplomats said UN sanctions had likely been violated.

"Clearly the facts still need to be established," said Britain's UN ambassador Mark Lyall Grant, though he added: "On the face of it, the transfer of these weapons to North Korea would be a violation of the sanctions."

Diplomats said Cuba should have sought a waiver to transfer the weapons, if they were obsolete.

They also said North Korea sanctions panel experts would take up the case but could require months to investigate it.

Shin In-Kyun, the president of the Seoul-based Korea Defence Network, said that while the North was capabale of repairing the weapons, it was possible it was importing parts for its own Soviet-era missiles.