SYDNEY: Australia's foreign minister on Wednesday confirmed for the first time that a dual Australian-Israeli citizen who died in a maximum-security Israeli prison had been working for Israel's government, and he raised the possibility of a diplomatic spat if the man's Australian passport was used for espionage.

Ben Zygier died in an apparent suicide in his prison cell in December 2010, and reports have said he had worked for the Mossad spy agency. Israel's government has refused to release details about the case even after a gag order was partially lifted that barred local media from reporting on it at all. Australia's government has said only that Zygier, an Australian who immigrated to Israel, had been charged with unspecified security offenses.

Foreign Minister Bob Carr said that Zygier was working for Israel's government, though he would not confirm or deny reports he had worked for Mossad. But Carr warned that the case raises serious questions about the use of Australian passports by dual nationals working for foreign governments, saying that if it's confirmed Israel used Zygier's passport for intelligence-gathering purposes, Australia would register "the strongest protest."

"Certainly if Australian passports were misused here, that's something we are forced to take very seriously," Carr told reporters. "No country can allow the integrity of its passport system to be compromised. We can't say whether it happened with Mr. Zygier's several passports. I hope the inquiry that takes place ... in Israel can clarify this position."

The mysterious case has strained relations between Australia and its close ally Israel, which suppressed all details of Zygier's imprisonment and death until Australia's national broadcaster broke the story last month. The Australian Broadcasting Corp. reported that Zygier, who had previously only been known as "Prisoner X," was a Mossad agent who hanged himself in what was supposed to be a suicide-proof solitary confinement cell.

The issue of misused passports is particularly sensitive for Australia. In 2010, an Australian investigation concluded that Israel had counterfeited four Australian passports used by a suspected hit squad that murdered a Hamas official in Dubai. Australia retaliated by expelling an Israeli diplomat.

Carr said there was no evidence Zygier was involved in the Dubai killing.

Carr ordered a review into how his foreign affairs department handled the case and released a report on Wednesday criticizing a lack of communication between Australian officials. The review also found that Zygier was granted regular access to a lawyer and was visited by family members more than 50 times during his imprisonment.

Carr said Australia has asked Israel to provide it with information on the charges Zygier was facing, but Israel has refused because of a gag order.