Moscow -- Prime Minister Vladimir Putin on Monday sought to calm Russian disputes with Poland over World War II, condemning the Nazi-Soviet pact and expressing sorrow over a Soviet massacre of Poles.

A day ahead of his visit to Poland to mark the outbreak of World War II, Putin described the 1939 Nazi-Soviet pact as "immoral," in stark contrast to the praise heaped on the agreement by some Russian figures in the last weeks.

Putin also acknowledged that the massacre of thousands of Polish officers by the Red Army at Katyn forest had been the subject of heavy emotion in Poland, amid continued anger at modern Russia's attitude towards the crime.

"Our duty is to remove the burden of distrust and prejudice left from the past in Polish-Russian relations," Putin said in an article he penned for the Polish daily Gazeta Wyborcza, a copy of which was published on the Russian government website Monday.

"Our duty... is to turn the page and start to write a new one."

The prime minister's comments came as he was expected in the Polish city of Gdansk on Tuesday to attend major ceremonies marking the 70th anniversary of the Nazi invasion of Poland that sparked World War II.

The visit comes amid severe tensions between Warsaw and Moscow over their shared history, most notably over the August 1939 pact between the Soviet Union and Nazi Germany that carved up Poland and the Baltic States ahead of the War.

"Without any doubt, it is possible to condemn -- and with good reason -- the Molotov-Ribbentrop pact concluded in August 1939," wrote Putin, referring to the two foreign ministers who signed the pact in the Kremlin.

"In our country, the immoral character of the pact was given an unequivocal evaluation by our parliament," he added in apparent reference to a 1989 condemnation of the pact by the Soviet Congress of People's Deputies.

"Today we understand that any form of agreement with the Nazi regime was unacceptable from the moral point of view and had no chance of being realised."

In the run-up to the 70th anniversary of the August 23, 1939 Nazi-Soviet Non-Aggression Treaty, top Russian historians have portrayed the deal as a canny move by Stalin that kept Russia out of the war for an extra two years.

According to a poll published by the Russian Public Opinion Study Center on Monday, only 22 percent of Russians believe World War II started in 1939.

Some 58 percent believe it started in 1941 with the Nazi invasion of the Soviet Union while five percent give other dates.

But Putin added that the Soviet Union had been pushed to sign the pact by the earlier 1938 Munich agreement signed by Britain, France and Italy with Hitler that had "destroyed all hope of the creation of a united front" against fascism.

He said that in the circumstances where the West "did not want to cooperate with the Soviet Union," Soviet diplomats "quite justifiably" decided that rejecting the pact would be a mistake.

Less than four weeks after the pact was signed Soviet troops invaded and occupied eastern parts of Poland.

In 1940 Soviet secret police massacred 22,000 Polish officers, intellectuals and others at Katyn forest in western Russia, a massacre Moscow for decades blamed on the Nazis.

"The Russian people, whose destiny was distorted by a totalitarian regime, also understand all too well the acute emotions of Poles in connection with Katyn, where thousands of Polish officers died," said Putin.

"We must together preserve the memory of the victims of this crime."

Russia's high court earlier this year threw out a bid by campaigners to reopen an enquiry into the 1940 massacre. It was only in 1990 that last Soviet leader Mikhail Gorbachev admitted the Soviets had killed the Polish prisoners.

AFP/Expatica