A Swiss museum said five artworks will be removed from public view on June 20 as it collaborates with the owner of the artworks to investigate whether the works were looted by Nazis during World War II.

On longterm loan to the Kunsthaus Zurich museum from collection owner the Foundation E. G. Bührle (or Bührle Foundation) the paintings in question are Jardin de Monet à Giverny by Claude Monet, Vincent van Gogh’s The Old Tower, La route montante by Paul Gauguin, Gustave Courbet’s Portrait of the Sculptor Louis-Joseph and Georges-Henri Manuel by Henri de Toulouse-Lautrec.

In a statement issued on Friday on its website, the museum said the Bührle Foundation requested the removal of the artworks as it assesses their provenance. The renewed scrutiny comes as a result of the U.S. State Department’s latest best practices for handling Nazi-looted art, published in March. These expand the Washington Conference Principles on Nazi-Confiscated Art set forth in 1998.

“The Kunsthaus welcomes this stance, but very much regrets that, with respect to our visitors, five of the pictures are being removed from the Kunsthaus’ rooms by the current owner, the Bührle Foundation,” the museum said. “The Bührle Foundation is acting comprehensibly and correctly in accordance with the agreement with the city of Zurich and in accordance with the provisions of the permanent loan agreement.”

“The Foundation strives to find a fair and equitable solution with the legal successors of the former owners for these works, following best practices,” said a statement in German from the Bührle Foundation.

The foundation said it is also conducting a separate investigation of a sixth work currently on display at Kunsthaus Zurich, Edouard Manet’s La Sultane.

“The work does not fall within the scope of [the U.S. State Department’s] “best practices” due to the sales processes, but is classified as a case that must be taken into account separately,” the foundation said in its statement. “Due to the overall historical circumstances, the foundation is prepared to provide symbolic compensation.”

Focused on French Impressionist and Post-Impressionist artworks, the Emil Bührle Collection, managed by the Bührle Foundation, is a core part of Kunsthaus Zurich’s offerings.

According to the museum website, the foundation’s loan of around 200 artworks “is permanent and can only be terminated with many years’ notice, for the first time at the end of 2034.”

Twenty-five countries, including Switzerland, have so far endorsed the expanded U.S. State Department guidelines for dealing with Nazi-confiscated art. The new agreement follows the 1998 Washington Conference Principles, which focused on providing restitution to the families of the original owners for treasures that were either stolen or forcibly sold by Nazis.

“Restitution should be to all lawful beneficiaries and heirs in accordance with a country’s usual inheritance law,” the March 2024 guidelines state. “All pre-War owners who are identified through provenance research or their heirs should be proactively sought by the current possessors for the purpose of restitution.”

Hundreds of thousands of paintings and millions of books as well as cultural and religious artifacts were stolen from Jewish owners by Nazis in the Holocaust. Many have still not been returned to their rightful owners.

According to a recent report by the World Jewish Restitution Organization and the Conference on Jewish Material Claims Against Germany, countries such as Russia, Romania, Spain, Denmark and Turkey have made scant progress in trying to restore looted artworks to the original owners or heirs over the past quarter of a century.

Although Switzerland remained neutral during World War II, it maintained strong economic ties to Nazi Germany and its allies.

“Confiscated artworks were often saved for private Nazi and German collections, while some pieces were sold to buyers through neutral countries like Switzerland to raise capital for purchasing additional art pieces and to purchase materials for the Nazi war machine,” states an article about Nazi looted art from the National Archives’ Holocaust Records Preservation Project. “Additionally, Switzerland offered a large market to sell off ‘degenerate art.’ “