United Nations inspectors are investigating a North Korean ship caught carrying arms from Cuba amid suspicion that the vessel is in breach of a wide-ranging arms embargo on North Korea.

A six-member UN team headed to the Howard Air Force Base on Tuesday for a three-day investigation into the undeclared arms shipment from Cuba after a request from the Panamanian government.

The experts will issue a report on whether the weapons violate a seven-year-old UN ban on arms transfers to North Korea because of its nuclear weapons and missile development.

Last month, Panama stopped the ship near the Atlantic entrance to the Panama Canal after receiving a tip it was carrying drugs, and seized the cargo after a standoff with the North Korean crew in which the captain tried to slit his own throat.

Officials have found most of the weapons Havana said were on board, including the two fighter jets, originally produced by the Soviet Union in the late 1950s, and two missile radar systems hidden under 10,000 tons of sugar on the freighter.

Before the arms were discovered, Cuba told Panama the cargo was a donation of sugar for the people of North Korea.

'Obsolete' weapons

Cuba later acknowledged it was sending 240 tons of "obsolete" weapons, including two MiG jets, 15 MiG engines and nine anti-aircraft missiles, to be repaired in North Korea and returned to Cuba.

On Tuesday, a government official said that Panama will likely return the 35-member crew of the ship, the Chong Chon Gang, to their native country in about a month.

"They're going to leave soon, like in a month, most likely they'll go back to Korea," the official told the Reuters news agency on the condition of anonymity. "There is another possibility that they're returned to Cuba and from there go to Korea."

The crew have been charged with threatening Panama's security by seeking to move undeclared weapons through the Panama Canal.

The Central American country will not respond to a request from North Korea seeking a "diplomatic manner" to resolve the future of the ship until the UN Security Council determines whether the shipment breached the embargo, which is aimed at curbing its nuclear weapons programme.

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