Israeli Prime Minister Ariel Sharon is still in the operating room, being treated for a massive brain hemorrhage after suffering what doctors said was a "significant" stroke late Wednesday.
The director, Shlomo Mor-Yosef of Hadassah Hospital in Jerusalem told reporters on Thursday that the surgery to stop the bleeding is likely to take several more hours.
He said Mr. Sharon was returned to the operating room after a CT scan revealed that he required more treatment, following a lengthy emergency surgery.
He described the 77-year-old prime minister's condition as "grave" and said he is sedated and on a respirator.
Government officials said Deputy Prime Minister Ehud Olmert had assumed the prime minister's duties while Mr. Sharon is unconscious. Mr. Olmert was to lead an emergency cabinet meeting on Thursday.
In Washington, President Bush said he is praying for Mr. Sharon's recovery.