The Cuban foreign ministry said the ship was carrying obsolete Soviet-era arms from Cuba for repair in North Korea.
The ship was seized by Panama last week after “undeclared military cargo” was found hidden in a shipment of sugar.
United Nations sanctions prohibit the supply of arms to North Korea in the dispute over its nuclear programme.
A Cuban foreign ministry statement said Cuba reaffirmed its commitment to “peace, disarmament, including nuclear disarmament, and respect for international law”.
It said the vessel was carrying 240 tonnes of obsolete defensive weapons — two anti-aircraft missile complexes, nine missiles in parts and spares, two MiG-21bis fighter planes and 15 MiG engines.
Cuba’s admission that it was sending weapons to North Korea for repair, in contravention of UN arms sanctions, explains part of the mystery surrounding this ship. But other questions remain.
Why not simply fly North Korean technicians and parts to Cuba to fix them instead of risking getting caught? Avoiding detection was obviously the plan when the ship had its AIS automatic transponder switched off when it left the Panama Canal to collect the Cuban weapons in June.
The ship itself, the Chong Chon Gang, has been caught in the past carrying narcotics and has had encounters with Somali pirates. But this latest episode gives just a small glimpse of some of the illegal maritime traffic going on all year round, unseen, across the world.
The Cuban statement said they were all made in the mid-20th Century and were to be repaired and returned to Cuba.
“The agreements subscribed by Cuba in this field are supported by the need to maintain our defensive capacity in order to preserve national sovereignty,” the statement went on.
Cuba said the ship’s main cargo was 10,000 tonnes of sugar.
The vessel left Russia’s far east on April 12 and travelled across the Pacific Ocean before entering the canal at the start of June, with Cuba as its stated destination.
Panamanian officials said the ship was carrying a cargo of sheet metal on its journey through the canal.
However, the vessel disappeared from satellite tracking systems after it left the Caribbean side of the canal, resurfacing on July 11.
Experts say this may indicate that the crew switched off the system that automatically communicates details of their location.
Panamanian officials tried to communicate with the vessel, suspecting it could be carrying illegal goods initially thought to be drugs.
The crew did not respond, so the ship was boarded and the weaponry was uncovered. (BBC)