The premier's spokesman said on Thursday that Olmert was due to be questioned for about one hour on Friday morning, and that he would "answer all questions put to him by investigators as he has on all previous occasions."

Media reports said Attorney General Menachem Mazuz took the unusual step of permitting an "urgent" interrogation under caution of Olmert at his residence.

Olmert is currently the subject of three police inquiries over possible corruption.

The cases involve potential conflicts of interest, fraudulent property transactions and abuse of power in connection with political appointments.

In November, police said they did not have enought evidence to continue a months-long investigation into allegations of abuse of influence over the sale of the country's second largest bank.

The probe had focused on suspicions that Olmert, when acting finance minister in 2005 under former prime minister Ariel Sharon, tried to steer the sale of Bank Leumi towards a friend, Australian real estate baron Frank Lowey.

Bank Leumi was eventually sold to another company with no relation to Lowey.