(Adds Australian government comment, former intelligence officer, paragraphs 12-16, 22-24)
LONDON, Feb 12 (Reuters) - An Australian man committed suicide in a high-security Israeli jail in 2010 after being held for months in great secrecy, Australia's ABC channel said on Tuesday, throwing new light on a case that has rattled Israel.
The unsourced Australian Broadcasting Corporation (ABC) story named the man, known previously only as "prisoner x", as Ben Zygier. It added that it "understood" the 34-year-old from Melbourne had been previously recruited by the Israeli spy agency Mossad.
Within hours of the report surfacing, Prime Minister Benjamin Netanyahu's office summoned Israeli editors to ask them not to publish a story "that is very embarrassing to a certain government agency", Israel's Haaretz newspaper said.
"The emergency meeting was called following a broadcast outside Israel regarding the incident in question," Haaretz said. Shortly afterwards, all reference to the Australian report vanished from Israeli news sites -- including Haaretz itself.
Such a gag order is highly unusual in Israel, where state military censors normally allow local media to quote foreign sources on controversial incidents -- such as an alleged attack on Syria last month by the Israeli airforce.
Members of the Israeli parliament in Jerusalem asked Justice Minister Yaakov Neeman to confirm if the report was true and demanded to know if other prisoners were being held in secret.
"This matter is not within the jurisdiction of the justice ministry," Neeman said. "There is no doubt that if this information is accurate this is something that ought to be checked," he added.
The state censors gave news outlets in Israel the green light to report the parliamentary debate but nothing else.
ABC said Zygier, who came from a prominent Jewish family in Australia, had moved to Israel 10 years before his death and had taken on the name Ben Alon. He married an Israeli woman and the pair had two children.
The Australian television channel gave no reason for his imprisonment, speculating only that it would have had to concern espionage and sensitive state secrets.
The man's family in Israel and Australia did not immediately respond to requests for comment.
Australian Foreign Minister Bob Carr said he was troubled by the accusations but Zygier's imprisonment had never been raised with Australian officials.
Zygier also carried an Australian passport in the name of Ben Allen, two foreign ministry officials said.
"I'm not reluctant to seek an explanation from the Israeli government about what happened to Mr Allen and about what their view of it is," Carr told Australian radio.
"The difficulty is I'm advised we've had no contact with his family there's been no request for consular assistance during the period it's alleged he was in prison," he said.
Carr said that, without a complaint from Zygier's family, the government was unable to act, while Australian diplomats in Israel knew of Zygier's jailing only after his death.
ABC said Zygier's imprisonment was so secret that not even his guards knew his name. However, word got out at the time of a mysterious prisoner being held incognito and human rights groups wrote to the state to demand more information.
"It is insupportable that, in a democratic country, authorities can arrest people in complete secrecy and disappear them from public view without the public even knowing such an arrest took place," the Association for Civil Rights in Israel wrote in June 2010.
When Israel's Ynet website wrote about the case that same month, the story was quickly removed because of a gag order.
Zygier was allegedly held in Ayalon Prison near Tel Aviv and was found hanged in his cell in December 2010. Funeral notices from Australia show that his body was flown back to Melbourne and that he was buried on Dec. 22.
Pictures of Zygier and his family remain on the Internet.
A former Australian intelligence official told the ABC that the country's domestic spy agency had for some time been watching Australian Jews suspected of working for Mossad because Australia's low international profile made them ideal recruits.
"Australians abroad are generally seen to be fairly innocent. It's a clean country. It has a good image like New Zealand," said former overseas spy agency official Warren Reed.
Australia's government complained to Israel in 2010 after faked Australian passports were used to stage the assassination in Dubai of a top Hamas operator and arms dealer.