Image caption Ben Zygier was identified last month by Australian media as the mysterious Prisoner X

Australia has confirmed for the first time that an Australian-Israeli man who died while secretly jailed in Israel worked for the Israeli government.

An official report also raised questions on the "misuse of Australian passports by Israeli intelligence".

The man was called Prisoner X by media because his identity and reasons for confinement were so secret.

He was recently identified in Australian media as Ben Zygier, who held dual citizenship.

Mr Zygier is believed to have been arrested in 2010 and held in secret in Israel's maximum security Ayalon prison.

Australian media say Ben Zygier was imprisoned because Israel suspected he had informed Australia's security agency of Mossad operations.

Timeline of Prisoner X scandal 10 Dec 2010: Man found hanged in cell at Ayalon prison

Story reporting brief details of the death appears on Israeli news website Ynet, but is then taken down

Rumours continue to circulate that Prisoner X, as he became known, was a Mossad agent

12 Feb 2013: Australia's ABC News names Prisoner X as Ben Zygier, 34

Mr Zygier was reportedly born in Melbourne to a prominent Jewish family and moved to Israel in 2000

13 Feb: Israeli justice ministry confirms the existence of Prisoner X

14 Feb 13: Australia admits it was told of Mr Zygier's detention in Feb 2010

He is reported to have hanged himself, aged 34, in the prison in December 2010. A post-mortem examination concluded he died of asphyxiation.

"Mr Zygier went off to live in another country, for 10 years, took out citizenship of that country, worked for its government," Australian Foreign Minister Bob Carr was quoted by AFP news agency as saying.

"And if reports are to be believed, he worked for one of its intelligence services. That's not something I can deny or confirm. You can draw your own conclusions."

Australian media have alleged that Mr Zygier changed his name several times and obtained numerous passports, which he used to do work for Mossad in Europe and the Middle East.

The ministry report however said: "There was no suggestion at the time or subsequently that Mr Zygier was involved in this misuse or that he obtained his passports fraudulently.

"But if media reports prove to be true that Mr Zygier used his passport in the service of Israeli intelligence, this would raise significant questions about the appropriateness of this activity."

Australia has previously complained to Israel about misuse of its passports. In 2010 it rebuked Israel after faked Australian passports were used in the assassination of a senior Hamas official in Dubai that year.