TEL AVIV (AFP) - Israeli former prime minister Ariel Sharon's health deteriorated further on Thursday, with his "vital organs" failing, the hospital where he has been housed in a comatose state for eight years announced.

"In the last few days, we have seen a gradual decline in the functioning of Ariel Sharon's vital organs, which are essential for his survival," Tel Hashomer hospital director Zeev Rotstein told Israeli public radio.

"His state is classed as critical, meaning his life is in danger," Mr Rotstein said.

"The medical staff and Sharon's family are expecting a turn for the worse," he added.

The 85-year-old's health worsened on Wednesday, as Mr Sharon suffered from "serious kidney problems" after undergoing surgery, Israeli media reported.

News website Ynet quoted medical sources as saying Mr Sharon was taken into intensive care a month ago. His health then stabilised but suffered a "significant deterioration" in the past few days.

The long-time leader of the rightwing nationalist camp in Israeli politics suffered a massive stroke on January 4, 2006, slipping into a coma from which he has never recovered.

Israeli and US specialists said in January 2013 that Mr Sharon had showed "significant brain activity" in an MRI scan, responding to pictures of his family seven years after the stroke.