Odyssey Marine Exploration of Tampa, Fla. -- which recovered the treasure last year -- said in a statement that what it has found is "apparently a cargo from a shipwreck as opposed to an actual vessel," the Tampa Tribune reported Friday.

Spain, however, says an analysis of the artifacts recovered by Odyssey shows the shipwreck is the Nuestra Senora de las Mercedes, a Spanish warship sunk by the British Navy south of Portugal in 1804.

The Spanish government is seeking in federal court the 17 tons of colonial-era coins worth an estimated $500 million, the newspaper said.

Court documents indicate Spain "has not abandoned or otherwise relinquished in any way its ownership of Mercedes."