"We plan to hear him by video conference tomorrow," federal prosecutor Friedrich Koenig told the Croatian commercial television network RTL on Wednesday.

Koenig told Austrian news agency APA that the Austrian authorities were also investigating a member of Sanader's family and a third person, but did not reveal their names.

Earlier on Wednesday, during a hearing before the Carinthian parliamentary commission investigating the Hypo Bank case, Sanader denied his friendship with Robert Jezic, the owner of the petrochemical company DIOKI, even though he was shown a letter written by the former chairman of the Hypo Bank board, Wolfgang Kulterer, to his successor, Til Berlin, which said that Jezic was "the best friend and ally of the Croatian prime minister," according to APA.

Sanader said it was possible that people were mentioning his name.

"The higher in the hierarchy a person is, the more often such things happen," Sanader said, adding that such things could not be controlled. He stressed that his closest ally and friend at the time was the present Prime Minister of Croatia, Jadranka Kosor.