Ehud Olmert, the Israeli Prime Minister, faced calls for his resignation today after admitting - in an apparent slip of the tongue - that Israel has got nuclear weapons.

But Israeli officials tried to push the cat back into the bag, denying that Mr Olmert had made any such admission and falling back on the Jewish state's policy of "nuclear ambiguity".

Widely considered the Middle East’s sole nuclear power, Israel has for decades refused to confirm or deny whether it possesses the atomic bomb. Mr Olmert appeared to break that taboo in an interview with a German television station as he began a visit to Berlin.

"We never threatened any nation with annihilation," Mr Olmert, speaking in English, told the N24 Sat1 station.

"Iran openly, explicitly and publicly threatens to wipe Israel off the map. Can you say that this is the same level, when they are aspiring to have nuclear weapons, as France, America, Russia and Israel?"

Mr Olmert’s spokeswoman, Miri Eisin, was quick to deny that the Prime Minister had admitted to Israel having nuclear weapons, saying that "Israel will not be the first country to introduce nuclear weapons to the region."

Israel's Negev nuclear research centre has been capable of creating nuclear-grade weapons material since the early 1960s, but has never been subject to inspection by the International Atomic Energy Agency.

The IAEA has said, however, that it considers Israel "to be a state possessing nuclear weapons" and proliferation experts reckon that it could have more than 100 devices.

Israel's policy of silence also allows it to skirt a US ban on funding countries that proliferate weapons of mass destruction and collect about $2 billion a year in military and other aid.

Mr Olmert's blunder came less than a week after Israeli officials rounded on Robert Gates, the incoming US Defence Secretary, for making the same slip-up during his Senate confirmation hearings.

"The staggering comments of Ehud Olmert only serve to reinforce the doubts on his capacity to remain Prime Minister," said Yossi Beilin, a leftist MP.

Yuval Steinitz, from the opposition Likud bloc, Yuval Steinitz called on Mr Olmert to step down after having made "an irresponsible slip which puts into question a policy that dates back almost half a century".

Meanwhile, observers warned that Mr Olmert’s statement threatened to undercut efforts by Israel and the West to prevent Iran from pursuing its nuclear programme, which Tehran says is for civilian purposes and the West fears is a cover for acquiring atomic weapons.

Mordechai Vanunu, who served 18 years in jail after blowing the whistle on Israel’s nuclear program in 1986, welcomed the comment.

"Olmert’s remark is nothing new, but it is a good thing that Israel decided to make it public," he told AFP.

"The world should now not only talk about Iran but also about Israel as a nuclear threat that has to be dealt in order to make a nuclear-free Middle East and bring peace."

In scrambling to contain the damage, Israeli officials said that Mr Olmert’s slip would not change the decades-old policy of silence on the country's nuclear capacity.

"I support the policy of ambiguity and I don’t see Olmert’s statement as a declaration that Israel has nuclear weapons," said Benjamin Ben-Eliezer, the Infrastructure Minister. "I would suggest that all those who want to talk about the issue, for God’s sake and for the sake of Israel’s security, stop it."

A senior Government official added: "This is a real slip of the tongue which was not planned. It is embarrassing for Israel particularly when it is dealing with such a sensitive issue. But this does not change a thing. Our policy stays the same."

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