Red Army soldiers raped two million German women, and thousands of Soviet women in occupied Eastern Europe, says a book published on Monday.
The author of Berlin: The Downfall 1945, the acclaimed military historian Antony Beevor, also suggests that after brutalisation in extreme war situations almost all men are tempted to become rapists.
But the book has been condemned as an "act of blasphemy" by the Russian ambassador to the UK and its conclusions have also been rejected by a prominent Russian military historian.
Mr Beevor, whose previous book Stalingrad became a best-seller, says in Berlin alone it was estimated up to 130,000 women were raped, of whom up to 10,000 committed suicide.
Altogether two million German women are believed to have been raped and almost half of those suffered gang rape.
Mr Beevor said he was shocked by what he found during his research of German and Soviet archives.
He said the widespread rape suggested "there is a dark area of male sexuality which can emerge all too easily, especially in war, when there are no social and disciplinary restraints."
He said the Soviet hierarchy turned a blind eye, and even condoned the rape as a form of revenge for what the German Army - the Wehrmacht - had done during Operation Barbarossa.
He said many people in Russia were still struggling to come to terms with what the Red Army did during the war.
Mr Beevor said: "I was shaken to the core when I discovered that soldiers raped female prisoners of war.
"That completely undermined the notion that they were only using rape as a form of revenge against the Germans.
The Wehrmacht had abducted many Russian and Ukrainian girls and set them up in "military brothels".
The Red Army, for its part, had engaged in an "alcohol-induced frenzy of sadism and humiliation".
He told BBC News Online: "One has this image of the Soviet state and the Red Army as being extremely disciplined but in the first four months of 1945 their soldiers were completely out of control."
Professor Oleg Rzheshevsky, head of war history at the Russian Academy of Sciences in Moscow, told BBC News Online these were grave accusations which were not supported by documentary evidence.
Professor Rzheshevsky, who admitted he had only read excerpts and had not seen the book's source notes, said: "Information on the number of raped and killed women is based on victims' and witnesses' accounts, some excerpts from interviews and other such sources."
Professor Rzheshevsky said considering what the German Army had done in the Soviet Union the Germans could have expected an "avalanche of revenge".
But he said that did not happen and added: "The majority of soldiers and officers of the Soviet Army and the allied armies treated the local population humanely."
Professor Richard Overy, a historian from King's College London, said the Russians had never faced up to the atrocities committed by the Red Army.
He said: "Partly this is because they felt that much of it was justified vengeance against an enemy who committed much worse, and partly it was because they were writing the victors' history."
http://news.bbc.co.uk/hi/english/world/ ... 939174.stm