Ammon News - JERUSALEM (Reuters) - Israel has secretly jailed a member of its security services for a grave offence, a prominent Israeli lawyer said yesterday, describing the case as riveting and sensational.

The revelation emerged from a memorandum released by the justice ministry on Monday on a previous secret detainee, the Australian Ben Zygier, an immigrant and disgraced Mossad spy who reportedly committed suicide in prison in 2010.

Avigdor Feldman, a lawyer who specialises in national security and who formerly advised Zygier - dubbed "Prisoner X" by the media - said that he knew of a second detainee, whom he described as "Prisoner X2".

Mr Feldman declined to elaborate on the second inmate other than to say he was male, Jewish, held Israeli citizenship and had worked for the government's secret services.

Asked how the second detainee's alleged offences compared with Zygier's, Mr Feldman told Tel Aviv radio station 103 FM: "Without getting into details? Much more grave. Much more sensational. Much more amazing. Much more riveting."

Zygier's case went public in February after it was reported in Australia, and the news of a second prisoner will expose the intelligence services to more unwelcome press attention.

Israeli officials have not published the charges against Zygier, saying only that he had endangered national security and had been held in isolation, with his own agreement, to avoid exposing him to media scrutiny while he prepared his defence.

After Australian television broadcast the Zygier affair, an Israeli court order prevented it being reported locally. The gags, which were enforced by military censors, have eased since.

The justice ministry on Monday published a previously redacted report on Zygier's suicide, which included mention of the second, unidentified, detainee held in another wing of the same prison.

No further information was provided by the ministry.