Gerd Honsik, 68, had already been sentenced to 18 months in prison in 1992 for propagating Holocaust denial in his book "Acquittal for Hitler?" However, he fled to Spain during his appeal and spent 15 years there before being extradited to Austria in 2007.

He now faces new charges for articles he allegedly wrote and circulated on the Internet.

The opening of his trial coincided with Nazi leader Adolf Hitler's 120th birthday - a fact that was not lost on the prosecution.

"One hundred and twenty years after Hitler's birth, there are still people denying his atrocities," prosecutor Stefan Apostol was quoted by national news agency APA as saying in his opening statement. "That's not just sad, it's dangerous."

Honsik pleaded innocent to the charges, saying he had no idea he was committing an offence when he disputed the existence of the Nazi gas chambers in his magazine, "Halt," in 1994. His lawyer, Herbert Schaller, also said that the existence of the gas chambers was "just the prevailing view" and called for relevant evidence to be presented.

Spain had twice rejected calls to extradite Honsik, saying Holocaust denial and neo-Nazi propaganda are not illegal in that country. He was finally extradited after two Europe-wide arrest warrants were issued at Austria's behest.