(JTA) — World Jewish Congress leader Ronald Lauder warned a Swiss museum to turn down the collection of masterpieces bequeathed to it from the Cornelius Gurlitt collection.

Lauder in an interview with Der Spiegel magazine published Saturday said the Kunstmuseum Bern would “trigger an avalanche of lawsuits” from potential claimants should it take the 20th century masterpieces. The claimants are the heirs of the collectors from whom some of the works may have been stolen by the Nazis.

He also criticized the slow pace of provenance research in German museums in general.

The museum’s board will make a decision by the end of November, a museum spokesman said.

Before Gurlitt’s death, some heirs had successfully sued to reclaim paintings. But it is not yet known how many works were confiscated or bought at depressed prices from their owners by the Nazis, for whom Gurlitt’s father, Hildebrand, was a collector in the late 1930s and early 1940s.

The collection came to light a year ago, when Focus magazine reported on the discovery made during the course of an investigation of Cornelius Gurlitt for tax evasion. Soon afterward, Germany established a commission to research the provenance of the works, including paintings by Max Beckman, Marc Chagall, Pablo Picasso, Henri Matisse and other 20th century masters.

Speaking for Germany in the same interview, Cultural Minister Monika Grutters agreed that progress was slow in general. But she confirmed that the German government was holding talks with the museum director in Bern and expressed confidence that a “good and reasonable solution” would be found for the collection.

The Swiss museum denied rumors in October that it already had accepted the collection.