JERUSALEM (AP) _ Israeli Prime Minister Ariel Sharon decided Tuesday that a whistleblower who spilled Israel's nuclear secrets will not be re-arrested after his release from prison but will be kept under supervision, a government statement said.

Mordechai Vanunu, a former nuclear technician, was sentenced to 18 years in prison for espionage after giving dozens of pictures and a description of what he said were nuclear weapons from Israel's top-secret Dimona reactor to London's Sunday Times in 1986. He is due to be released in April.

Israeli officials are concerned that Vanunu could disclose further secrets after his release, and some have been looking at ways to silence him. Proposals include keeping him under administrative detention, barring him from traveling overseas and preventing him from appearing in public.

In a meeting with the defense and justice ministers and other officials, Sharon decided that the Vanunu needs to be kept under supervision to prevent him from ``committing further security offenses,'' the statement said, without giving details.

Israel's official policy about nuclear weapons is purposely ambiguous. Officials say only that Israel will not be the first to introduce them into the Middle East.

But based on Vanunu's pictures, experts concluded Israel had the world's sixth-largest stockpile of nuclear weapons. The CIA estimated more recently that Israel has between 200 and 400 nuclear weapons.

Since his arrest, Vanunu has become the poster figure for critics of Israel's nuclear program.

He has been repeatedly nominated for the Nobel Peace Prize, and an American couple adopted him in the mistaken belief that this would entitle him to U.S. citizenship and hasten his release.