JERUSALEM: Speculation was widespread in Israel last night over the identity of a mysterious prisoner being held for unspecified crimes in the maximum security Ayalon jail.

Dubbed ''Mister X'' by the Hebrew language news website Y-net, the man's identity has even been kept from his guards.

A measure of the severity of the crimes for which the man in being held is the fact that he is being housed in the cell that was built for Yigal Amir, the assassin of the former Israeli prime minister Yitzhak Rabin.

According to Y-net, nobody knows who the man is and with what he has been charged. Nobody talks to him, nobody sees him, nobody visits him, nobody knows he is in jail.

''He was placed in full and complete separation from the outside world,'' one prison service official quoted by Y-net said.