The captain of a treasure-hunting ship that Spain intercepted in a dispute over a US $500 million (euro350 million) undersea find was released Wednesday after being questioned, the skipper's company said.

The American captain, Sterling Vorus, was detained after the Odyssey Explorer was seized Tuesday as it sailed into Spanish waters from the British colony of Gibraltar, off Spain's southern tip, police said.

Vorus was held by Civil Guard overnight, after refusing to allow police aboard his ship for a search, Odyssey co-chairman Greg Stemm told The Associated Press.

Police were searching the vessel on Wednesday, he said.

The dispute began when Odyssey, a Tampa, Florida-based company that specializes in deep-sea shipwreck recoveries, announced the discovery of a colonial-era shipwreck in May and said coins found on the vessel had been flown to the United States from Gibraltar.

Spain filed claims in a U.S. federal court over the find, arguing that if the shipwrecked vessel was Spanish — or the treasure removed from its waters — the find belonged to Spain.

Culture Minister Cesar Antonio Molina said the government viewed Odyssey as modern day pirates. "There have always been navies, laws and the rule of law to help combat pirates," Molina told journalists at Spain's Senate.

Odyssey has insisted the shipwreck was in international waters, but has not given an exact location or a ship's name.

Another Odyssey vessel involved in the treasure hunt off Gibraltar, the Ocean Alert, was seized, searched and released after a week in July.

In both cases the Civil Guard said it was acting on orders from a Spanish judge who in June instructed authorities to seize vessels belonging to Odyssey Marine Exploration if they sailed from Gibraltar.

Stemm insisted Odyssey's activities were legitimate and transparent. "This whole thing is so crazy," he said.

Stemm would not comment on Spanish media reports that Odyssey had removed high-tech equipment from the Odyssey Explorer before it was boarded by Civil Guard investigators.