Moscow's deal with Hitler was "immoral," Vladimir Putin wrote in an article for Poland's daily Gazeta Wyborcza. But he also blamed other European nations for leaving the Soviet Union to face Nazi Germany alone.
Putin, on the eve of his visit to Poland for war anniversary ceremonies, reiterated his support for a new collective security treaty to replace NATO that would include all of Europe, the United States and Canada.
He also struck a conciliatory note on the 1940 massacre by Soviet secret police of Polish military officers and intellectuals in Russia's Katyn forest and other locations.
Putin, German Chancellor Angela Merkel and other European leaders are to attend the ceremonies Tuesday at Westerplatte, a former Polish military outpost that held off a Nazi attack over the first week of the German invasion.
For Poles, this Baltic Sea peninsula has come to symbolize their wartime heroics.
Nazi Germany sparked the war by invading Poland on Sept. 1, 1939, just days after its Foreign Minister Joachim von Ribbentrop signed a mutual nonaggression treaty with his Soviet counterpart, Vyacheslav Molotov.
Soviet troops then invaded Poland 16 days later, in what the Poles call a "stab in the back," acting on the deal with Hitler to divide Europe.
But Putin argued Moscow had no choice, blaming Western leaders for failing to oppose Hitler's appetite for territorial expansion.
"Without a doubt there are full grounds to condemn the Molotov-Ribbentrop pact of August 1939. But after all, a year earlier France and England signed a well-known agreement with Hitler in Munich, destroying all hope for the creation of a joint front for the fight against fascism," Putin wrote.
Putin said the Munich treaty encouraged Hitler by showing he would face no opposition. Poland, however, argues it was the Molotov-Ribbentrop deal that sparked the war that engulfed the globe, taking more than 40 million lives, including six million Polish citizens.
Putin insisted the legacy of the war served as an example of the importance of including Moscow in all European security architecture.
"All the experience of the period between the wars ... convincingly shows that it is impossible to create an effective collective security system without the participation of all countries of the continent, including Russia," he said.
Yet Putin also struck a conciliatory note with Poland - a former Soviet satellite-turned European Union member - saying that the grief caused by the 1940 murder of more than 20,000 Polish prisoners of war by the Soviet NKVD struck a cord with the average Soviet citizen, who also suffered under totalitarianism.
"To the people of Russia, whose fate has been deformed by a totalitarian regime, the sensitivity of Poles over Katyn, where thousands of Polish soldiers lie, is well understood," Putin wrote in what appeared to be an unusually strong criticism of the Soviet government from him.
Putin called for "joint grief and forgiveness" in the hope that "Russian-Polish relations will sooner or later reach such a high level of true partnership," as Russian-German ties.
Before the anniversary ceremonies, Putin is to meet with Polish Prime Minister Donald Tusk for much awaited talks on bilateral economic issues. Tusk is also expected to raise the sticky points, like the Katyn massacre.
Polish prosecutors trying to pursue the perpetrators say they are getting no support from Moscow, which they say refuses to declassify relevant files.
Putin was in Poland as president in 2005 for the 60th anniversary of the liberation of the German death camp of Auschwitz by the Red Army, but held no political talks.