Mordechai Vanunu, whose 18-year prison term ends in April, wrote in a letter published on Tuesday he was lured by a young woman to agents who drugged, bound and shipped him from Rome to Israel.

Israel has said it may confiscate his passport when he is released next month. Vanunu was nabbed by the Mossad in Europe in 1986 after he gave details and photos of Israel’s top-secret nuclear plant in the Negev Desert to The Sunday Times of London.

An Israel court convicted him of treason and espionage. He spent more than a decade in solitary confinement.

It was unclear how the letter, first broadcast on Israel’s Channel Two late on Monday and republished in the Maariv daily on Tuesday, passed through prison censorship. Israeli defence ministry officials were not immediately available to comment.

It is widely believed - based on photographs Vanunu provided the British newspaper - Israel has the sixth largest stockpile of nuclear weapons in the world. The CIA recently estimated Israel has between 200 to 400 atomic weapons.

Israel has an official policy of "nuclear ambiguity,"saying only that it will not be the first to introduce nuclear arms to the Middle East.

In the letter, Vanunu wrote he would not "concede or fold, regret or apologise, be deaf or shut up".