A patrol of the Spanish navy expelled from the Alboran Sea a U.S.-owned, Panamanian-flagged vessel that was allegedly carrying out soundings to find sunken ships, authorities said Friday.

The ship that was made to leave had done most of its work Thursday at some 25 miles from the Malaga coast, an area of international waters but part of the Spanish continental platform.

The navy's Infanta Cristina patrol boat performed an inspection of the commercial ship, with the agreement of its captain, to determine whether it was engaged in illicit activities.

During the search, Spanish naval personnel found that the ship contained technical equipment specialized in finding sunken vessels, such as a sidescan sonar that can create images of large areas of the sea floor.

After the search and interrogation, the Spanish patrol ordered the treasure hunters to cease their activities in compliance with the United Nations Agreement on the Law of the Sea and the United Nations World Heritage Convention, after which the commercial ship left the area.

Two planes carrying $500 million in treasure salvaged from the 19th-century Spanish frigate Nuestra Señora de las Mercedes arrived in Madrid in February after Spain won a nearly five-year-long legal battle against a U.S. treasure-hunting firm. EFE