Ben Zygier – the Mossad agent who killed himself two years ago after being secretly held in Israel’s most secure prison– had fed details about his missions to the Australian security services it has been claimed.

Israeli-Australian Zygier was known only as "Prisoner X" until a week ago when Australia’s ABC television identified him and claimed that he worked as a spy.

The same channel said that Zygier had met members of the Australian Security Intelligence Organisation (Asio) – Australia’s secret service - during four trips home, and that he disclosed comprehensive details about his missions within the Mossad.

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The Israeli government has refused to comment on Zygier, only belatedly confirming his identity but not that he was a Mossad operative and otherwise ordering newspapers not to report details of the case. If the ABC claims are correct, the Zygier case represents a serious breach for the agency.

It is believed that Zygier was one of three Israeli-Australian agents who took advantage of the Australian law that allows people to change their name every 12 months, and apply for a new passport each time. When Zygier’s body was returned to Australia, just weeks after the birth of his second daughter, it was under the name Ben Allen.

ABC believes that Mossad was particularly concerned that Zygier had revealed details of a complex mission in Italy, which involved setting up a fake electronics company and selling equipment to, among other, the Iranians. It is not clear to what extent the mission was a success, why Zygier decided to inform the Asio and how he got caught. The Australian government has been criticised for not providing sufficient support to Zygier when he was arrested, and has launched its own investigation into the affair.

Zygier was an enthusiastic Zionist who moved to Israel in the 1990s, after which he was recruited by the Mossad. The agency was eager to recruit those that had dual nationality, allowing them to travel freely on another country’s passport, without ever needing to identify themselves as Israeli.

Mossad used passports from several countries during an operation in early 2010 when a Hamas commander Mahmoud Mabhouh, who acted as an arms trader for the group, was killed in a Dubai hotel. Details of several of the fake passports were made public, and learning that an Australian passport had been used, Canberra expelled an Israeli diplomat in protest.

Zygier died in December 2010 after apparently hanging himself in solitary confinement cell, which was fitted with CCTV and designed for Yigal Amir the killer of then Israeli Prime Minister Yitzhak Rabin. Such was the secrecy surrounding his case that not even his prison guards were aware of his name.

Israeli government officials say that the secrecy surrounding Zygier’s case was tested up to the supreme court, which was persuaded by the government’s national security argument. A spokesman refused to comment on the ABC claims; it is believed that the Israeli government has no plans to comment further on the case.

On Sunday, Israeli Prime Minister Benjamin Netanyahu acknowledged the case but defended the need to keep some information out of the public domain, citing Israel’s security needs.

“We are not like all other countries,” Mr Netanyahu said. “We are more threatened, more challenged, and therefore we have to ensure the proper activity of our security forces. Allow the security forces to work quietly so we can continue to live securely and safely.”