The US Senate has increased pressure on Poland to compensate Jewish families for property confiscated from Polish-Jewish citizens during and after the Holocaust.

On Monday, 88 senators from both sides of the aisle signed a letter to Secretary of State Mike Pompeo asking him to “help Poland resolve the issue comprehensively”.

Poland is the only country in the European Union that has not passed a comprehensive law for the restitution of or compensation for private property that was taken from Jewish citizens by the Nazis, the letter said.

It comes as Germany returned nine works of art to descendants of a Jewish couple more than 80 years after they were stolen by the Nazis.

The artworks – which consisted of paintings, casts and a wooden panel – were confiscated in Munich in 1938. The return ceremony took place at the Bavarian National Museum in Munich, where Bernd Sibler handed over the pieces. 

The senators' letter on Poland noted that, although originally confiscated by the Nazis and not the Polish state, property owned by Jews as well as non-Jews was nationalised by the communist regime that took over after the Second World War.

“In the decades since the fall of the Iron Curtain, Jewish Holocaust survivors of Polish origin and their families as well as others have found it nearly impossible to reclaim or seek compensation for the property that was nationalized by the Polish Communist regime,” the letter said.

The senators added that it was “deeply troubling” that Polish Prime Minister Mateusz Morawiecki had said his country had already resolved the issue.

The bipartisan effort led by the Republican Marco Rubio and Democrat Tammy Baldwin gained an unusually large number of signatories on the issue, including Democratic presidential candidates Bernie Sanders, Elizabeth Warren, Kirsten Gillibrand, Kamala Harris and Cory Booker.

Leading Republicans such as Lindsey Graham, Ted Cruz, Rand Paul and Mitt Romney also signed.

Eric Gallagher, representative of the World Jewish Restoration Organization in Washington, said the letter “demonstrates once again that the United States Congress has not forgotten about Holocaust survivors and remains steadfast in pursuing justice for them.”