Olmert is expected to be replaced by Israeli Foreign Minister Tzipi Livni who won a narrow victory in the ruling Kadima party election earlier this week.

Livni received 43.1% of the vote, 2% ahead her main rival, Transport Minister Shaul Mofaz, becoming Kadima's first woman and only its third leader since former prime minister Ariel Sharon founded the party in November 2005.

Olmert, who faces corruption and fraud charges, earlier pledged to resign as soon as the new party leader is chosen. However, he is to stay on as caretaker prime minister until a new coalition government has been formed.