Marking the anniversary, Polish Prime Minister Donald Tusk said in an X post: "On March 5, 1940, a decision was made in Moscow to murder over 22,000 Polish war prisoners. May the memory of the Russian lie and Katyn crime be a warning for the world."
He added: "Let us always call it as it is: a crime is a crime, a victim - a victim, an aggressor - an aggressor."
Officials have said that the root cause of that decision of March 5, 1940, was a secret agreement between the Soviet Union and Nazi Germany known as the Molotov-Ribbentrop Pact.
According to historians, that agreement opened the door to those two countries invading Poland in 1939 and paved the way to the horrors of World War II.
Following the Soviet invasion of Poland in September 1939, thousands of Polish officers were deported to camps in the Soviet Union.
Some 22,000 Polish prisoners of war and intellectuals were killed in the spring of 1940 on orders from top Soviet authorities in what is known as the Katyn Massacre.
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Source: IAR, PAP, ipn.gov.pl