Odyssey Marine Exploration/AP

Giles Tremlett - The Guardian

US officials offered to help Spain claim an undersea treasure haul of gold and silver coins discovered by a controversial American exploration company in return for Spanish assistance in the recovery of valuable art looted by Nazi Germany, according to embassy cables released by WikiLeaks.

In a conversation with the Spanish culture minister, César Antonio Molina, the US ambassador in Madrid, Eduardo Aguirre, sought to tie the treasure found off the Iberian peninsula by Odyssey together with attempts by an American citizen, Claude Cassirer, to recover a painting by Camille Pisarro that hangs in a Madrid museum.

"The ambassador noted also that while the Odyssey and Cassirer claim were on separate legal tracks, it was in both governments' interest to avail themselves of whatever margin for manouevre they had, consistent with their legal obligations, to resolve both matters in a way that favoured the bilateral relationship," the embassy reported in a cable on 2 July 2008.

The offer was made after the Spanish government claimed ownership of half a million gold and silver coins found on the floor of the Atlantic Ocean by Odyssey's underwater robots. The company had provoked Spanish fury by landing the treasure at Gibraltar and flying it straight to the US.

The so-called Black Swan treasure, which Odyssey said came from an unidentified shipwreck, had been valued at about $500m.