Heirs of Jewish art collectors who lived in Nazi Germany are suing Germany in a US court, hoping to win back treasure of enormous value.

The plaintiffs, Alan Phillip, from London, and Gerald Stiebel from Santa Fe, filed a lawsuit on Monday against Germany and the Prussian Cultural Heritage Foundation at a District of Columbia court.

According to their lawyers, they reverted to US justice because they felt that they had reached a dead end in Germany.

Last year, the German advisory board for Holocaust-related claims - the Limbach Commission - rejected their claim that the 1935 sale of the treasure to Nazi Germany had been forced. But the ruling did not keep the plaintiffs from pursuing their goal.

Mr Phillip and Mr Stiebel want the restitution of a collection of medieval relics known as the 'Welfenschatz' or the 'Guelph Treasure', valued today at about 200 million euros (£147m). They have been trying to get the treasure back since 2008.

Their ancestors, the Frankfurt-based dealers Zacharias Max Hackenbroch, Isaac Rosenbaum, Saemy Rosenberg and Julius Falk Goldschmidt, bought the 82-item collection in 1929 as an investment. Over the following two years, the men sold about half the items to museums and collectors in the US and Europe, but these pieces made up only 20 per cent of the value of the collection, the plaintiffs claim.

Nazi Germany purchased the remaining items in 1935 for what the plaintiffs say was a deflated price, in a sale orchestrated by Hitler's deputy, Reichsmarschall Herman Goering.

In their suit, the plaintiffs say that the sale in 1935 "relied on the atmosphere of early Nazi terror, in which German Jews could never be arms-length commercial actors."

Prussian Cultural Heritage Foundation President Hermann Parzinger said on Tuesday that he was "astonished by this step" and was sure that "any court ruling on its merits would reach the same conclusion that we and the Advisory Commission have reached".