Former US President Jimmy Carter has said Israel holds at least 150 nuclear weapons.

This is the first time a former US president has publicly acknowledged the Jewish state's atomic arsenal.

Asked at a news conference at Wales's Hay literary festival on Sunday how a future US president should deal with the Iranian nuclear threat, Carter put the risk in context by listing atomic weapons held globally.

"The US has more than 12,000 nuclear weapons, the Soviet Union (Russia) has about the same, Great Britain and France have several hundred, and Israel has 150 or more. We have a phalanx of enormous weaponry ... not only of enormous weaponry but of rockets to deliver those missiles on a pinpoint accuracy target," he said, according to a transcript of his remarks.

While the existence of Israeli nuclear weapons is widely assumed, Israeli officials have never admitted their existence and US officials have stuck to that line in public for years.

The Nobel Peace Prize winner said Washington should talk directly to Tehran to persuade it to drop its nuclear ambitions.

Years of US policy, including sanctions and a debate about the possibility of military strikes, have not persuaded Iran to abandon its ambitions to produce enriched uranium.

President George W Bush has branded calls for negotiations with Iran's president as comparable to the appeasement of Adolf Hitler before World War Two.

A former Israeli military intelligence chief criticised Carter's comments and said they would do more harm than good.

"It seems to me that in his last tour of the country and the region, he was apparently so offended that he thought it proper to say things which I think are irresponsible," said Aharon Zeevi-Farkash.

"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.

Carter visited the Middle East in mid-April, during which he met the leader of the Islamist group Hamas in Syria to try to move a peace process forward between Israel and the Palestinians.

Israeli Prime Minister Ehud Olmert refused to meet Carter, who has been critical of Israeli policy towards the Palestinians, during a regional visit that began on April 13.

Carter was president from 1977 to 1981. During that time, he helped negotiate a peace treaty between Israel and Egypt and concluded a strategic arms agreement with the Soviet Union. - Reuters