Medical experts warned Monday that former Israeli Prime Minister Ariel Sharon's deteriorating condition could put his life in danger, while the hospital where he is being treated said more tests would be run to determine the cause for his downturn.

The Sheba Medical Center near Tel Aviv, where Sharon is being treated, released a statement late Sunday saying the former leader's kidneys were failing and that changes were detected in his brain membrane. Sharon, 78, has been in a coma since suffering a severe stroke in January.

The hospital said more tests were being run to determine what had caused the change in his condition. A spokeswoman refused to say whether his life was threatened.

Two of Sharon's former aides, who said they spoke to his son Gilad, said Sunday there was no immediate danger to the former leader's life. The former aides spoke on condition of anonymity because they were not authorized to discuss the matter with the media.

But Dr. John Martin, a cardiovascular expert at London's University College, said the kidney failure and the changes in the brain membrane that Sharon has suffered in the past two days indicate the former leader's life is in danger. His comments were echoed by other physicians quoted in Israeli media.

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Kidney dialysis and drugs to treat what appears to be cerebral edema could lead to an improvement in Sharon's condition within hours, Martin said. But many physicians would choose not to take such steps when a patient has been in a coma for more than seven months, he added.

"This is a significant decrease in his condition," Martin told The Associated Press. "Shall we give dialysis or shall we let him die ... most European physicians would consider this at this point."

Sharon, Israel's most popular politician, had a small stroke in December and was put on blood thinners before he suffered a severe brain hemorrhage in January. The Israeli leader underwent several, extensive brain surgeries to stop the bleeding, and many independent experts doubted he would ever recover.

The last surgery on Sharon, in April, was to reattach a part of his skull which was removed during the emergency surgery to reduce pressure on his brain. The reattachment was described as a necessary step before transferring Sharon to the long-term care facility at Sheba hospital.

Sharon personified Israel's military might for decades, and Israelis were stunned to see him felled by illness.

His stroke came after Sharon saw through his contentious plan to withdrawal Israel from the Gaza Strip after 38 years, and just two months after Sharon shook up the Israeli political map by bolting his hard-line Likud Party to form the centrist Kadima faction.

After the stroke, Sharon's successor as party leader, Ehud Olmert, led Kadima to victory in a March 28 vote and became prime minister.