Jerusalem ? Ariel Sharon underwent five hours of emergency brain surgery Friday that doctors said successfully stopped a hemorrhage and relieved swelling inside his skull. Officials said his condition showed “significant improvement” but experts said the prognosis remained dire.

Sharon’s chief surgeon told The Associated Press it was too early to assess how much damage the prime minister suffered after two similar operations in as many days. That determination will have to wait until at least Sunday, when doctors plan to wean him off the drugs that are keeping him in a state they described as a medically induced coma.

Acting Prime Minister Ehud Olmert took calls Friday from Secretary of State Condoleezza Rice and Egyptian President Hosni Mubarak, a sign that the Israeli government was moving ahead without its hard-charging leader. Sharon’s Kadima Party said it would rally around Olmert, and a new poll showed Kadima emerging victorious in March 28 elections under his leadership.

Palestinian leaders said they were in touch with officials about Sharon’s condition.

But experts not involved in Sharon’s care said he may have fallen into a coma by himself as a result of the massive hemorrhagic stroke he suffered Wednesday while en route to the hospital. In that case, Sharon might not regain consciousness when the drugs are withdrawn. Interaction with the patient is required to assess some aspects of brain function.