The existence of a second "Prisoner X" being held in top-secret conditions in an Israeli jail has prompted comments in the Israeli parliament and media.
The case was revealed in legal documents released this week concerning the original "Prisoner X", an Australian-Israeli who hanged himself in his prison cell in 2010.
He has been identified as Ben Zygier, a disgraced Mossad spy.
The second prisoner is also said to involve a member of security services.
The Knesset's chairman of the Committee on Defence and Foreign Affairs, Avigdor Lieberman, told parliamentarians the case was "extremely serious" but insisted Israeli prisoners' rights were protected.