Spain formally laid claim Thursday to a shipwreck that yielded a $500 million treasure, saying it has proof the vessel was Spanish. Officials demanded the return of the booty recovered last year by a U.S. deep-sea exploration firm, saying the 19th-century shipwreck at the heart of the dispute is the Nuestra Senora de las Mercedes - a Spanish warship sunk by the British navy southwest of Portugal in 1804 with more than 200 people on board. Tampa, Fla.-based Odyssey Marine Exploration on Thursday disputed Spain's claim. In May 2007, Odyssey announced that it had discovered a wreck in the Atlantic - and its cargo of 500,000 silver coins and other artifacts worth an estimated $500 million.

At the time, Odyssey said it did not know which ship it was, and flew the treasures back to Tampa without Spain's knowledge, from an airport on the British colony of Gibraltar on Spain's southwestern tip.

The company said Thursday that there isn't enough evidence to prove the vessel is the Mercedes. Officials said in a company statement that they found only cargo from a shipwreck, not the actual vessel.

The Spanish government filed evidence in a Tampa federal court to support its claim.

"We are talking about the remains of a Spanish navy vessel and the human remains of Spanish naval servicemen who died on board which have been illegally disturbed," Culture Ministry Director General Jose Jimenez said.

"It is the property of the Spanish navy, government and people, and we want it all back," said Adm. Teodoro de Leste Contreras, who runs a naval museum owned by the ministry.

Washington-based lawyer James Goold, representing the Spanish government in the case, said U.S. Judge Mark Pizzo will convene the two parties to review the case before deciding who gets to keep the treasure.

Goold said at a Madrid news conference that he expected Odyssey would keep "not a penny" of the salvage.

In its statement, Odyssey officials said they are surprised the Spanish government has conclusively said "the "Black Swan" treasure is from the Mercedes after viewing site photomosaics and video that show no hull, ballast pile, keel or vessel, and only a statistically insignificant sample of the coins from the site."

Naval and coin experts say they have proof that the treasure, now held in a warehouse in Tampa, came from the Mercedes. The coins included gold doubloons, or "pieces of eight," minted in 1803 in Lima, Peru, bearing the image of Spain's King Carlos IV, ministry coin expert Carmen Marcos said.

But Odyssey officials said that if the coins are found to be from the Mercedes, it will be "up to the U.S. District Court to determine the final disposition of the Black Swan treasure," according to the statement.

The Mercedes exploded and sank in a naval battle as it sailed back to Spain from South America.

Spain argues that the entire treasure should be returned because naval vessels remain the property of the nation that flagged them, regardless of where they lie, under the principle of sovereign immunity.

"Spain has not abandoned or otherwise relinquished in any way its ownership of Mercedes," Spain's petition said.

Spain's claim said artifacts on the seabed, their distribution and other characteristics, as well as artifacts taken by Odyssey, "further identify the site as the remains of Mercedes."

Odyssey also said the ship was probably the Mercedes after Pizzo last month forced the company to disclose information on the salvage, including the identity of the ship and its location.