Vienna, Austria ? Austrian prosecutors appealed a three-year prison sentence for right-wing British historian David Irving, saying Tuesday the punishment was too soft for his strident denial of the Holocaust.

Irving pleaded guilty Monday to denying the mass killings of Jews in World War II concentration camps, a crime in the country of Hitler’s birth. Austria’s 1992 law applies to “whoever denies, grossly plays down, approves or tries to excuse the National Socialist genocide or other National Socialist crimes against humanity in a print publication, in broadcast or other media.”

The law calls for a prison term of up to 10 years.

“The public prosecutor believes the ruling was too lenient in light of a possible sentence of up to 10 years and Irving’s special importance to right-wing radicals,” said Walter Geyer, spokesman for the public prosecutor’s office in the capital, Vienna.