Ex-US President Jimmy Carter has said Israel has at least 150 atomic weapons in its arsenal.
The Israelis have never confirmed they have nuclear weapons, but this has been widely assumed since a scientist leaked details in the 1980s.
Mr Carter made his comments on Israel's weapons at a press conference at the annual literary Hay Festival in Wales.
He also described Israeli treatment of Palestinians as "one of the greatest human rights crimes on earth".
Mr Carter gave the figure for the Israeli nuclear arsenal in response to a question on US policy on a possible nuclear-armed Iran, arguing that any country newly armed with atomic weapons faced overwhelming odds.
"The US has more than 12,000 nuclear weapons; the Soviet Union (sic) has about the same; Great Britain and France have several hundred, and Israel has 150 or more," he said.
"We have a phalanx of enormous capabilities, not only of weaponry but also of rockets to deliver every one of those missiles on a pinpoint accuracy target."
Most experts estimate that Israel has between 100 and 200 nuclear warheads, largely based on information leaked to the Sunday Times newspaper in the 1980s by Mordechai Vanunu, a former worker at the country's Dimona nuclear reactor.
The US, a key ally of Israel, has in general followed the country's policy of "nuclear ambiguity", neither confirming or denying the existence of its assumed arsenal.
However, Israeli Prime Minister Ehud Olmert included Israel among a list of nuclear states in comments in December 2006, a week after US Defence Secretary Robert Gates used a similar form of words during a Senate hearing.
Former Israeli military intelligence chief Aharon Zeevi-Farkash told Reuters news agency he considered Mr Carter's comments "irresponsible".
"The problem is that there are those who can use these statements when it comes to discussing the international effort to prevent Iran getting nuclear weapons," he said.
During the press briefing, Mr Carter expressed his support for Israel as a country, but criticised its domestic and foreign policy.
"One of the greatest human rights crimes on earth is the starvation and imprisonment of 1.6m Palestinians," he said.
The former US president cited statistics which he said showed the nutritional intake of some Palestinian children was below that of children in Sub-Saharan Africa, as well as saying the European position on Israel could be best described as "supine".
Mr Carter, awarded a Nobel Peace Prize in 2002, brokered the 1979 Egypt-Israel peace treaty, the first between Israel and an Arab state.
In April he controversially held talks in the Syrian capital Damascus with Khaled Meshaal, leader of the militant Palestinian movement Hamas.
The former US president's Carter Center was unavailable for further comment.