A confidant of Prime Minister Ehud Olmert says the Israeli leader will step down "immediately" after his party chooses a successor this month.

The comment shoots down speculation that Olmert would try to linger in office for months.

Olmert has already announced plans to resign in order to battle a corruption investigation. But he has been unclear when he would actually step aside.

Olmert's Kadima Party is scheduled to hold a primary next Wednesday, though the party could hold a runoff if no candidate receives 40 percent of the vote. Cabinet ministers Tzipi Livni and Shaul Mofaz are the front-runners.

The Olmert confidant says the Israeli leader will formally resign "immediately following the primary."

He spoke on condition of anonymity because the Israeli leader has not made his plans public.