Former Israeli Prime Minister Ariel Sharon, comatose since a 2006 stroke, has deteriorated to a "life threatening" condition after suffering kidney malfunction, Israel Radio said.
Officials at the hospital near Tel Aviv where the 85-year-old has been treated, did not comment.
A Health Ministry spokeswoman also declined to comment.
The ex-general and right-wing leader was known for executing a dramatic political about face with a 2005 Gaza pullout that turned Israeli politics on its head when he quit his party and created a centrist faction that ruled Israel for several years.
The radio, echoing reports by other Israeli media outlets, said Mr Sharon's condition had worsened in the past several days and that his life was in danger due to kidney failure.
The Haaretz newspaper's Web site quoting an unnamed source said that Mr Sharon could die in "a matter of days" if his condition continued to decline.
Israel's Channel 2 television said Mr Sharon's sons were at his bedside.