It is one of the most dramatic collections of medieval church treasures in the world, but now the drama has once again spilled over to the courts. In the latest turn in the long running saga surrounding the Guelph Treasure, attorneys acting on behalf of two heirs of the Jewish art dealers who once owned the collection have filed a lawsuit in the US District Court in Washington, D.C., claiming the treasures were sold under Nazi duress.

The treasures, also known as the Welfenschatz, are valued at $250 million (220 million euros) and include many outstanding goldsmith works from the Middle Ages. Among them are ornate gold containers, gem-encrusted crosses and the portable altar of Eilbertus of Cologne. Some date back to the 11th century.

Originally assembled over the centuries by the Braunschweig Cathedral in northern-central Germany, the works eventually passed into the hands of the Guelph family, Europe's oldest royal dynasty, in 1671. In 1929, Duke Ernst-August von Braunschweig-Lueneburg sold a consortium of Jewish art dealers 82 pieces - of which 42 were sold again six years later, in 1935, to the German state of Prussia, governed by senior Nazi official Hermann Goering.

"Any transaction in 1935 where the sellers on the one side were Jews and the buyer on the other side was the Nazi state itself is by definition a void transaction," acting attorney Nicholas O'Donnell said at a press conference in Berlin on Tuesday. The plaintiffs are listed as Alan Philipp from London and Gerald Stiebel from Santa Fe, New Mexico.

The fresh lawsuit follows a failed claim filed by the two in 2008 through Germany's Limbach Commission, a state-backed advisory body that oversees the return of cultural property seized as a result of Nazi persecution. Last year the commission ruled that the collection was not a "forced sale due to persecution."

In February the city-state of Berlin registered the collection of gold relics in the Index of Valuable National Assets, meaning it may no longer leave Germany without approval of the country's culture minister.

The Guelph collection is managed by the Prussian Cultural Heritage Foundation and has been on display since the 1960s in Berlin's Museum of Decorative Arts.

jgt/kbm (dpa/ap)