Panamanian investigators searching a North Korean ship detained for carrying undeclared Cuban arms have found two military jet fuselages.

Two Soviet-era MiG-21 fighter jets were discovered inside containers on board, along with anti-aircraft radars, which the Cuban government says were part of a range of “obsolete” weapons being sent to North Korea for repair.

Prosecutor Javier Caraballo said the supersonic planes gave off a strong odor of gasoline, indicating that they had likely been used recently, reports Reuters.

Officials said seven containers had been unloaded and opened so far, but they suspected more were still hidden underneath the ship’s official cargo of 10,000 tonnes of sugar, according to BBC.

The Chong Chon Gang was seized on July 15 on suspicion that it was carrying drugs, but instead authorities found military equipment: potential breach of a UN arms embargo on North Korea.

North Korea reiterated the arms were part of a legitimate deal with Cuba and demanded the immediate release of the vessel, which Panama has so far dismissed.

The 35 North Korean crew members has also been charged with “crimes against Panama’s internal security for trafficking undeclared arms.”