He has questioned the use of large-scale gas chambers to exterminate the Jews and has claimed that the numbers of those who perished are far lower than those generally accepted. He also contends that most Jews who died at Auschwitz did so from diseases like typhus, not gas poisoning.
Irving remained in custody Thursday at a prison in Graz, 120 miles south of Vienna, the Austria Press Agency reported, although that could not be confirmed.
If formally charged, tried and convicted, he could face up to 20 years in prison, said Otto Schneider of the public prosecutor's office.
But Schneider said it was unclear whether there were sufficient legal grounds to continue holding Irving on such a charge so many years after the alleged offense was committed. A decision was expected by the end of next week on how to proceed, Schneider said.
In March, more than 200 historians from around the world petitioned C-SPAN to cancel a project that would have included a speech by Irving as a counterpoint to a lecture by Deborah Lipstadt, a renowned Holocaust expert at Emory University.
Irving once sued Lipstadt for libel for calling him a Holocaust denier, but his lawsuit was dismissed in 2000 by a British court, which ruled that Irving was anti-Semitic and racist and misrepresented historical information.
His film, "The Search for the Truth in History," triggered protests in Australia that led organizers of the Melbourne Underground Film Festival to cancel a screening.
Irving has had numerous run-ins with the law over the years. In 1992, a judge in Germany fined him the equivalent of $6,000 for publicly insisting the Nazi gas chambers at Auschwitz were a hoax.
