Panama said on Wednesday it had called on the UN Security Council to investigate a North Korean ship caught smuggling arms from Cuba, piling more pressure on Pyongyang over a possible breach of UN sanctions.

Panama stopped the ship last week and seized its cargo after a stand-off with the North Korean crew in which the captain tried to slit his own throat. Authorities discovered missile equipment, MiG fighter jets and other arms aboard that Cuba said were "obsolete" Soviet-era weapons being sent to North Korea for repair.

"It's going to be transferred to the UN Security Council. They will decide what to do," Panamanian Security Minister Jose Raul Mulino said in Panama City.

Five UN investigators, including one from the Security Council, are expected to arrive around the beginning of August once the ship, the Chong Chon Gang, has been unloaded, Panamanian government officials said.

The North Korean government urged Panama to release the ship and its crew, who were detained and are in the process of being charged for failing to declare the arms on board.

"This cargo is nothing but aging weapons, which are to send back to Cuba after overhauling them according to a legitimate contract," a North Korean Foreign Ministry spokesman was quoted as saying by the official KCNA news agency.

The incident has not derailed US-Cuban talks on migration, which went ahead as scheduled on Wednesday, but US officials said Washington would raise the issue of the ship with Cuba very soon. One senior US lawmaker called the matter a "grave violation of international treaties."

The United Nations has imposed various sanctions on Pyongyang, including strict regulations on arms shipments, for flouting measures aimed at curbing its nuclear weapons program.

UN Secretary-General Ban Ki-moon praised Panama on Wednesday for seizing the vessel, adding that the UN sanctions committee would take up the issue promptly.

About 350 police and border patrol officials were combing through the ship, which has a dead weight of some 14,000 tonnes.

Before their arrest, the ship's crew burned the electrical system to disable it, which slowed the process of unloading it, a Panamanian Foreign Ministry spokesman said. As a result, it could take up to 10 days to unload the ship, he added.

"This ship was loaded so you can't unload it," security minister Mulino said on his Twitter account.

Two more containers with suspected arms have been found on the ship in addition to the two already discovered.

Access points to the ship's storage areas were all "completely blocked" in breach of international regulations, when Panamanian officials boarded it, Mulino said.

Britain's UN Ambassador, Mark Lyall Grant, said the ship appeared to have violated the UN arms embargo. Britain is a permanent member of the UN Security Council.

An eight-member panel of experts appointed by Ban Ki-moon monitors the Security Council sanctions imposed on North Korea.

The experts are mandated to "gather, examine and analyze information from States, relevant United Nations bodies and other interested parties" on allegations of sanctions violations and report back to the 15-member Security Council.

Crew Tight-Lipped

Marie Harf, a spokeswoman for the US State Department, said Panama had asked the United States for technical assistance on the matter, which would be provided. She said Washington would be talking to Cuba "very soon" about the ship.

A State Department official said the scheduled migration talks with Havana went ahead on Wednesday as even though the United States believes Cuba broke UN sanctions, the issues were deemed to be "apples and oranges."

According to Cuba, the weapons on the ship included two anti-aircraft missile batteries, nine disassembled rockets, two MiG-21 fighter jets, and 15 MiG-21 engines, all Soviet-era military weaponry built in the middle of the last century.

Servicing of weapons would also be in breach of the arms embargo imposed on North Korea sanctions.

A UN resolution adopted in 2009 says the embargo applies to "all arms and related materiel, as well as to financial transactions, technical training, advice, services or assistance related to the provision, manufacture, maintenance or use of such arms, except for small arms and light weapons."

US Democratic lawmaker Robert Menendez, the Chairman of the Senate Foreign Relations Committee, issued a statement condemning Cuba, saying it needed very careful monitoring.

"The shipment ... is a grave violation of international treaties," he said. "Weapons transfers from one communist regime to another hidden under sacks of sugar are not accidental ... and reinforces the necessity that Cuba remain on the State Department's list of countries that sponsor state terrorism."

Hal Klepak, a history professor at the Royal Military College of Canada, said Cuba was "using weapons and equipment of staggeringly old vintage" and that the Pentagon had long since written off the island as a military threat.

Since Cuba's military doctrine was designed to deter any attack, it needs to maintain the arms it has, he added.

"Cuba cannot afford to buy anything newer and does not have repair facilities of its own for such needs. Thus if it is not to scrap, for example, the aircraft entirely, it must repair and potentially update them in some areas," Klepak said.

Panama's Foreign Minister Nunez said his country had no problem with Cuba but had been under a UN obligation to stop the North Korean vessel and inspect its contents.

Javier Caraballo, Panama's top anti-drugs prosecutor, said 33 of the 35 crew members had so far been charged with crimes against Panama's internal security for trafficking undeclared arms. All 33 members had invoked their right to remain silent, he added. The government said it aims to charge all the crew.

Separately, IHS Fairplay, which monitors the movement of ships, said it had found another North Korean-flagged vessel made a similar journey to Chong Chon Gang last year. The O Un Chong Nyon Ho docked in Havana during May 2012, IHS said.

Ends/AMA/18/07/13