Two Israeli MPs on Tuesday questioned the justice minister over reports about the mysterious 2010 death of an Australian prisoner with suspected Mossad ties whose identity was kept top secret.
"This prisoner was detained under a name which was not his own. Do you know about this?" Arab Israeli MP Ahmed Tibi asked during an open question session in the Knesset, or parliament.
"Can you confirm that this Australian committed suicide in prison under a false name so it wouldn't be revealed he was being detained in Israel?" he asked outgoing Justice Minister Yaakov Neeman.
Similar questions were raised by the head of the leftwing Meretz party, Zehava Gal-On who asked Neeman if he considered it "normal that the prime minister's office should summon all the main media to avoid the publication of any information likely to embarrass Israel."
Until now, a complete media blackout has been imposed on the shadowy incident, with the Israeli press prevented from reporting the incident due to a strict gag order.
In response to the parliamentary questions, Neeman said he was not able to answer "because the justice ministry is not responsible for prisons".
"But there is no doubt that if true, the matter must be looked into," he added.
The story of Prisoner X first emerged in May 2010 when Israel's Ynet news website ran a story entitled "Who are you, Mr X?" in which it spoke about a prisoner being held in top secret conditions whose identity and crime was not even known to his jailers.
But the story was quickly taken offline due to a gag order.
Earlier on Tuesday, Australia's ABC news ran a story identifying the mystery prisoner as an Australian national from Melbourne who was recruited by Israel's Mossad spy agency.
The channel named the man as Ben Zygier, 34, but said he was known in Israel as Ben Alon.
It said the case of Prisoner X had come to be regarded as one of the most sensitive secrets of Israel's intelligence community with a tight gag order imposed on all details of the case.
Zygier had been living in Israel for about 10 years prior to his arrest in early 2010 and was married with two children, according to the channel, which said he had been recruited by Mossad.
It was not clear why he was arrested in "early 2010" but he was taken to Ayalon Prison in Ramle near Tel Aviv and held in the same cell used for the man who shot dead former Israeli prime minister Yitzhak Rabin in 1995.
There he was held in virtual isolation until his "apparent suicide" in December that year, the channel said.
After the Ynet article was published, the Association for Civil Rights in Israel wrote to complain to Israel's attorney general saying: "It's alarming that there's a prisoner being held incommunicado and we know nothing about him."
In response, the attorney general's office wrote back saying: "The current gag order is vital for preventing a serious breach of the state's security, so we cannot elaborate about this affair."
The ABC report said Zygier's body was found hanged despite "state-of-the-art surveillance systems," adding to the mystery surrounding the affair.
His body was flown to Melbourne where it was buried in a Jewish cemetery on December 22, 2010.
Zygier's relatives and friends declined to comment to ABC.