Jailed British historian David Irving has again said he does not believe Hitler presided over a systematic attempt to exterminate Jews in Europe.
During his trial in Austria, Irving said he had changed his mind over claims the Holocaust did not happen.
But, speaking from his cell later, he told BBC News the numbers killed at Auschwitz were smaller than claimed.
He is appealing for a reduction in the three-year jail term. Prosecutors are seeking for it to be lengthened.
The Austrian state prosecutor's office said it believed Irving's sentence for Holocaust denial was too lenient in light of a possible sentence of up to 10 years.
The prosecutor also deemed the sentence too light because of "Irving's special importance to right-wing radicals", a spokesman for the office said.
The historian pleaded guilty in his one-day trial in Vienna on 20 February.
In court, the 67-year-old admitted that in 1989 he had denied that Nazi Germany had killed millions of Jews.
Speaking from prison, where he is in solitary confinement for 23 hours each day, Irving told BBC Radio 4's Today programme he now believed there had been cases of Jewish people being gassed during World War II.
But he said that while he accepted 1.4 million were killed in the so-called "Operation Reinhard" camps which included Treblinka and Sobibor, he did not accept that large numbers were murdered at Auschwitz.
He claimed there were two "small" gas chambers there, not the large-scale gas chambers identified by other historians.
"Given the ruthless efficiency of the Germans, if there was an extermination programme to kill all the Jews, how come so many survived?" he said.
When asked whether there was an organised programme to exterminate the Jews in Europe, overseen by Hitler, Irving told Today: "That is absolutely wrong and nobody can justify that.
"Adolf Hitler's own involvement in it has a big question mark behind it."
The trial against Irving arose from comments he made in Austria in 1989 denying the existence of gas chambers at Auschwitz.
Austria is one of 11 countries with laws against denying the Holocaust.
The historian previously said that he doubted the Holocaust's existence until he saw the personal files of Adolf Eichmann, the chief organiser of the Holocaust.
Gas chamber 'hoax'
"I said that then based on my knowledge at the time, but by 1991 when I came across the Eichmann papers, I wasn't saying that anymore and I wouldn't say that now," Irving told the court.
"The Nazis did murder millions of Jews."
In the past, he had claimed that Adolf Hitler knew little, if anything, about the Holocaust, and that the gas chambers were a hoax.
Irving's lawyer has said his client is unlikely to serve the full three-year term because of various factors, including his age.
Speaking on Today, Richard Evans, professor of German history at Cambridge University and a witness against Irving at a libel trial in 2000, dismissed the latest comments.
"He was, I think, arrogant enough to believe that he wouldn't be arrested," said Professor Evans.
"But having said that, I think the Austrian action is ill-advised. I don't think that law which bans Holocaust denial is really necessary any longer and I think it's really regrettable the vast media circus that's surrounding Mr Irving now [is] just simply giving prominence to his absurd views."