A UN team launched a probe Tuesday to determine whether a shipment of Cuban arms found hidden aboard a North Korean freighter violated UN sanctions, officials said.
The Chong Chon Gang was boarded and searched July 10 as it passed through the Panama Canal, on suspicion it was carrying drugs.
Instead, inspectors uncovered an undeclared shipment of Cuban weapons, including two Soviet-made MiG-21 fighters. Havana later said they were being shipped to North Korea to be refurbished.
"The UN mission is in the country now and began work early," Security Minister Jose Raul Mulino told AFP.
The UN experts will report on their findings to the UN Security Council, which must decide whether the shipment violates a ban on arms transfers to North Korea.
The six member team is led by David Martin Uden, a former British ambassador to South Korea and currently coordinator of the UN experts group charged with monitoring enforcement of sanctions against North Korea.
The weapons systems were found in 25 containers buried under tons of sugar.
Besides the MiGs, the shipment included anti-aircraft and guidance systems, missiles, explosives and command-and-control vehicles.
Cuba said the weapons systems were "defensive and obsolete" and were being shipped to North Korea for refurbishment under a legitimate contract.
Thirty-five North Korean sailors have been detained on arms trafficking charges that carry maximum sentences of up to 12 years in prison.
The ship is moored at the port of Colon, but Panamanian authorities have kept secret for security reasons where the arms shipment is being held.