Father Gabriele Amorth who is Pope Benedict XVI’s ‘caster out of demons’ made his comments during an interview with Vatican Radio.
Father Amorth said: "Of course the Devil exists and he can not only possess a single person but also groups and entire populations.
"I am convinced that the Nazis were all possessed. All you have to do is think about what Hitler – and Stalin did. Almost certainly they were possessed by the Devil.
"You can tell by their behaviour and their actions, from the horrors they committed and the atrocities that were committed on their orders. That’s why we need to defend society from demons."
According to secret Vatican documents recently released wartime pontiff Pope Pius XII attempted a "long distance" exorcism of Hitler which failed to have any effect.
Father Amorth said: "It’s very rare that praying and attempting to carry out an exorcism from distance works.
"Of course you can pray for someone from a distance but in this case it would not have any effect.
"One of the key requirements for an exorcism is to be present in front of the possessed person and that person also has to be consenting and willing.
"Therefore trying to carry out an exorcism on someone who is not present, or consenting and willing would prove very difficult.
"However I have no doubt that Hitler was possessed and so it does not surprise me that Pope Pius XII tried a long distance exorcism."
In the past Father Amorth has also spoken out against the Harry Potter books, claiming that reading the novels of the teen wizard open children’s minds to dabbling with the occult and black magic.
Father Amorth, who is president of the International Association of Exorcists, said of the JK Rowling books:"Behind Harry Potter hides the signature of the king of the darkness, the devil."
He said that Rowling’s books contain innumerable positive references to magic, "the satanic art" and added the books attempt to make a false distinction between black and white magic, when in fact, the distinction "does not exist, because magic is always a turn to the devil."
Father Amorth is said to have carried out more than 30,000 exorcisms in his career and his favourite film is, according to Italian newspapers The Exorcist.