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, he asked BBC News why, if such a programme existed, "so many survived".

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 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 Monday.

In his trial, 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 News he now believed there had been isolated cases of Jewish people being gassed during World War II.

However, he added that "Hitler's own involvement has a big question mark behind it", before repeating his belief that an extermination policy did not exist.

"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.

The charges 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.

PHOTO CAPTION

Historian David Irving appears in court in Vienna with handcuffs with his 1977 book 'Hitler's War'. (AFP)