Mariusz Klarecki said it was difficult today to estimate the number of artworks looted or destroyed by Soviet forces following the USSR's invasion of Poland on September 17, 1939, the anniversary of which fell on Sunday.
"The subject of the destruction and looting committed by the Soviet Union against Polish cultural assets has still not been sufficiently researched and described," he said. "Many issues remain a great unknown to us."
Mariusz Klarecki said it was difficult today to estimate the number of artworks looted or destroyed by Soviet forces following the USSR's invasion of Poland on September 17, 1939.
When the USSR invaded eastern Poland, many cities associated for centuries with culture fell into Soviet hands, including Grodno, Lviv and Vilnius, which were all then part of Poland.
Klarecki explained that after September 17, the looting and destruction took place in several stages, starting with private homes and palaces as well as churches, public buildings and museums. He said the looting was committed both by individual Red Army soldiers and by specialist 'trophy battalions' created for the purpose.
The art historian said the second phase started in January 1944 and continued through 1945-1946 and included territories that became part of Poland after the war, such as Lower Silesia in the south and Mazury in the northeast.
He said the third phase of looting occurred in the closing stages of the war and immediately after it ended, when the Soviet trophy battalions looted art from eastern Germany that had previously been stolen from Poland by the Nazis.
"According to international law, Russia is obliged to return Polish cultural assets looted during the war," Klarecki explained. "Cases of the plunder of cultural assets have no statute of limitations - not only in the ethical and moral dimension but also in the sphere of international law. Restitution is an ongoing and endless process. The Polish state will never stop seeking and recovering cultural assets that were stolen as a result of the Second World War."