The ARA Libertad was detained Oct. 2 in the port of Tema as collateral for unpaid bonds dating from Argentina's economic crisis a decade ago. Argentina appealed to the U.N.'s International Tribunal for the Law of the Sea for the ship's release, arguing that as a warship the Libertad is immune from being seized.
There was no comment from judicial authorities in Ghana about the ruling.
In an expedited ruling, the court ordered that Ghana "forthwith and unconditionally release the frigate ARA Libertad" and ensure the ship and its crew can leave Ghanaian waters. It also ordered that the vessel be resupplied as needed.
Detaining the ship was "a source of conflict that may endanger friendly relations among states," the court said.
The ruling left untouched the parties' rights to seek further international arbitration on the matter.
Argentine Economy Minister Hernan Lorenzino hailed the decision and vowed to continue fighting what President Cristina Fernandez has called "vulture funds," with which the country is locked in a series of legal battles.
"Argentina will continue to defend itself from the financial pirates," Lorenzino said via Twitter on Saturday. "Vultures, you won't succeed, with the ship nor with the debt."
Ghana courts ordered the ship held on a claim by Cayman Islands-based NML Capital Ltd. Its owner, American billionaire Paul Singer, leads a group demanding payment in full, plus interest — about $350 million — for dollar-based Argentine bonds bought at fire sale prices after Argentina's 2001-2002 economic collapse forced a sharp devaluation of its currency.
The vast majority of bondholders accepted about 30 cents on the dollar years ago, and that is roughly what the holdouts led by Singer initially paid for the bonds.
In an emailed statement, NML criticized the tribunal for making a ruling.
"The Ghanaian courts have sole jurisdiction over this dispute, and that is where this matter has been and will continue to be lawfully heard," it said. "It is completely inappropriate for the International Tribunal for the Law of the Sea to attempt to interfere with orderly proceedings of the independent judiciary of Ghana."
Susana Ruiz Cerutti, the head of Argentina's delegation to the tribunal, was quoted by the Telam state news agency as praising the ruling for being unanimous and for siding with the vessel's captain, who had been accused of contempt.
It wasn't immediately clear how soon, or if, the ship would be allowed to set sail. The director-general of the Ghana Ports and Harbors Authority, Richard Anamoo, told The Associated Press that "it is not the port authorities that are holding the ship. We were only implementing a (Ghanaian) court order."
Argentina defence minister, Arturo Puricelli, said at a news conference in Buenos Aires that a charted plane would deliver 98 more sailors to Ghana on Wednesday to join the skeleton crew that stayed with the Libertad. He estimated the sailing ship could return to Buenos Aires by Jan. 9.
Associated Press writers Almudena Calatrava in Buenos Aires and Francis Kokutse in Accra, Ghana, contributed to this report.