The remarks by Medvedev, which coincide with the celebration of Victory Day in the country on Saturday, reflect increasing frustration in Russia with the position of its ex-Communist Bloc western neighbours towards the conflict.
"We are all the more often encountering what are called historical falsehoods. Also such attempts are becoming tougher, more malicious and aggressive," Medvedev said in comments on his video blog.
"It seems that time is distancing us more and more from the war."
"We must not close our eyes to the terrible truth of war. And on the other side we cannot allow anyone to put the heroic deed of our people into doubt," he said.
Western historians of the period have long irritated Russia by emphasising how strategic errors by wartime dictator Joseph Stalin and brutal purges of his top officials complicated the Soviet victory over Nazi Germany.
Ukrainian President Viktor Yushchenko in 2007 posthumously decorated Roman Shukhevych, the leader of the Ukrainian Insurgent Army (UPA), a controversial group that fought Soviet security forces and was accused of Nazi collaboration.
No-one however disputes the Soviet Union's suffering in the war -- according to the Russian authorities 8.6 million Soviet soldiers and 27-28 million civilians were killed in the conflict.
Medvedev said that while it was natural that different interpretations of the war would emerge over time, Russia now had to prove again the "historical truth" of the conflict.
"This is hard and sometimes even, to be honest, disagreeable. But it has to be done."
His comments come as the government considers putting a controversial bill towards parliament that would make it a crime to "rehabilitate Nazism" by denying the Soviet victory in World War II.
Ruling party lawmaker Varely Ryazansky said earlier this month that the government should hand the bill to parliament in June and it was expected to receive cross-party support, the RIA Novosti news agency reported.
However some liberal observers have condemned the planned law -- initiated by long serving cabinet minister and ruling party stalwart Sergei Shoigu -- as a needless move that could be used against freedom of speech.
In a sign the debate still arouses passions, the Novaya Gazeta newspaper this week published for the first time letters by prominent Soviet writer and war veteran Viktor Astafyev bitterly critical of the Soviet leadership.
"Only criminals could have messed up their own people in such a way. Only enemies could have led an army like this during a war. Only idiots could have held an army under fear and suspicion," he wrote in a letter from 1990.
Russia, whose increasingly assertive behaviour under Medvedev and his predecessor Vladimir Putin has worried the West over the past years, is to mark the 64th anniversary of the Soviet victory over Nazi Germany with a military parade in Red Square.
The parade, annual fixture in the Soviet Union which sees nuclear-capable missiles shown off in the centre of town, was revived last year following an order by Putin.
The revival of the parade by Putin -- who also restored the music for the Soviet national anthem -- is a throwback to the days when Soviet leaders would peer at the proceedings from the top of Lenin's mausoleum.
Source: AFP Global Edition