The questioning led several Knesset members to advise Olmert to voluntarily step back from duties as prime minister while investigations continue, the Israeli newspaper Haaretz reported.

It was reported that Shula Zaken, who has been Olmert's secretary for 30 years, was questioned by authorities Tuesday, the Jerusalem Post reported Friday.

The court reportedly put a gag-order on the investigation, forbidding the public from being officially informed about the nature of Friday's questioning.

"The prime minister intends to fully cooperate with law enforcement officials, as he has in the past, and he is convinced that once the truth is disclosed in the framework of the police investigation, the suspicions against him will disappear," a statement from the Prime Minister's Office said.