Seventy years ago, an estimated 22,000 Polish soldiers were executed by the Soviet Union's secret police, the NKVD, in the Katyn forest in Russia.

On April 7, Russian Prime Minister Vladimir Putin and his Polish counterpart, Donald Tusk, will mark the Katyn massacre officially for the first time.

Polish Foreign Minister Radoslav Sikorski has described the meeting as "another step towards Polish-Russian reconciliation."

For years, the Soviets blamed German Nazis for the killings, and it was only in 1990 that then-Kremlin leader Mikhail Gorbachev admitted his country's responsibility.

Gruesome events

Following the division of Poland between Hitler and Stalin, Polish officers found themselves in 1939 under Soviet captivity. The Russian secret service feared the Poles would rise up against Moscow, so Stalin gave his blessing to a mass execution, which started on April 3, 1940.

Three years later, the Germans found parts of the mass graves in Katyn near Smolensk, and used the find to fuel anti-Soviet propaganda. The exiled Polish government, then in London, broke off contact with the Kremlin.

After of the war, Stalin tried to cover up the crime. In addition to the mass grave in Katyn, others were detected in Piatykhatky and Mednoe. As the Soviets blamed German Nazis for the war crimes, the truth was buried for decades.

Polish-Russian tensions

Since Gorbachev admitted the Soviet responsibility, there has been tension between Moscow and Warsaw over the Katyn massacre. High-ranking Russian officials still claim the murders were not committed by the Soviet Union.

Russian justice authorities in 2004 refused to re-open an inquiry into the massacre, claiming part of the documents were a state secret.

An Oscar-nominated film made in 2007 by a Polish director about the massacres has only ever been screened twice in Russia. The father of the director, Andrej Wajda, was among those murdered.

cb/ns/dpa/AFP/epd
Editor: Toma Tasovac