The Second World War Katyn massacres were committed on the direct order of Soviet dictator Josef Stalin, Russia's lower house of parliament has said - a statement hailed by Polish officials.
The 1940 massacre of around 20,000 Polish officers and other prominent citizens in western Russia by Soviet secret police has long soured relations between the two countries. President Dmitry Medvedev will visit Poland in early December.
Soviet propaganda for decades blamed the killings on the Nazis, but post-Soviet Russia previously acknowledged they were carried out by the People's Commissariat for Internal Affairs, or NKVD - Stalin's much-feared secret police.
The statement passed by the State Duma appears aimed as a step towards Russia definitively breaking with its Soviet legacy. Some observers have expressed alarm in recent years that Russia may be quietly rehabilitating Stalin. Last year, a quote praising Stalin was restored to the decoration of one of Moscow's busiest subway stations; this year, Moscow's mayor proposed allowing posters depicting Stalin as part of the annual celebrations of the defeat of Nazi Germany.
"This historic document is important not only for Russian-Polish relations - much more it is important for us ourselves," said Konstantin Kosachev, chairman of the Duma's foreign relations committee, according to the news agency ITAR-Tass.
Russia has turned over scores of volumes of documents this year about Katyn to the Polish government.
"Published materials, held in secret archives for many years, not only reveal the scale of this awful tragedy but show that the Katyn crime was committed on the direct order of Stalin and other Soviet leaders," says the statement, which also expresses "deep sympathy for the victims of this unjustified repression".
Communist legislators tried to amend the statement to remove the naming of Stalin, but were defeated.
"The falsification of history that we are fighting against in other countries is also taking place in our country, and today we could see it with our own eyes," Mr Kosachev said of the amendment attempt. Russian officials frequently use the term "falsification of history" to attack perceived attempts to underplay the importance of the Red Army in the fight against Nazi Germany.
The head of the Polish parliament's foreign affairs committee, Andrzej Halicki, said he considered the Duma's statement to be a breakthrough. However, Jaroslaw Kaczynski, head of the conservative opposition Law and Justice party, said he still wants Russia to offer a full apology and compensation.