Does it matter? Would it make much difference if Israel now dropped its policy of ambiguity and said that it had nuclear weapons?

Yes, a bit, and enough to make that shift unwelcome, say Western officials and analysts. Anything that might provoke extra Arab interest in nuclear programmes is unwelcome; it would also distract attention from Iran’s ambitions.

But those concerns are ones of image and diplomacy. The presumed reality of Israel’s weapons capability has influenced the tense calculations of the region for years. The new and more destabilising factor is Iran, and whatever its own studied ambiguity, its presumed intention is to acquire the option of nuclear weapons.

Yesterday’s fuss over what Ehud Olmert actually said had the air of a one-day row, but a long day at that. In an interview with the N24 cable news channel in Germany on Monday, Olmert asked about Iran’s nuclear programme, said that the US, France, Britain and Russia had nuclear weapons but were “civilised countries that do not threaten the foundations of the world”. He then added: “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 America, France, Israel, Russia?”

A storm of articles in the Israeli press yesterday mused over whether Olmert’s remark represented a deliberate change of policy, many authors displaying perfect ambivalence themselves. In an analysis in Yedioth Ahronoth, Ronen Bergman asked “Is this a deliberate dispelling of the ambiguity or amazing coincidence? It’s hard to say.”

Speculation that this was indeed a change, intended to warn Iran, and perhaps prompted by the US, was provoked by a similar comment earlier this month from Robert Gates, President Bush’s new Secretary of Defence. In his Senate confirmation hearing, Gates said: “They [Iran] are surrounded by powers with nuclear weapons — Pakistan to their east, the Russians to the north, the Israelis to the west and us in the Persian Gulf.”

Olmert himself, appearing embarrassed, yesterday said in Berlin, to an excited Israeli press corps, that “I stress that the state of Israel will not be the first country in the Middle East to introduce nuclear weapons”, in three separate answers with slight variations.

An Israeli government spokesman yesterday added that “there is no change in the well-known Israeli policy”. Mark Fitzpatrick, proliferation analyst at the Institute for Strategic Studies in London, said that the remark “produced such consternation in the Foreign Ministry” that he assumed it was a slip of the tongue.

Fitzpatrick is among those arguing that Israel’s formal acknowledgement of having nuclear weapons would be undesirable. The formalising of its status might put future options out of reach, he suggested, such as Israel concluding that it had enough fissile material and shutting down its reactor.

Gary Samore, at the Council on Foreign Relations in New York, also argued that declaration would increase the risk of a regional nuclear arms race. “I do think that if Israel formally confirmed [having weapons] it would put more pressure on Arab countries to develop their own — which they are threatening to do anyway because of Iran.”

He is sceptical that declaration would do anything to boost the chances of an eventual regional arms deal, given that Israel is not likely to give up its weapons, and Iran’s refusal to recognise its right to exist.

Officials and analysts argue that even if undeclared, Israel’s weapons retain their value as a deterrent because everyone believes that it has them. That assumes, in Iran’s case, that the regime can be deterred in the conventional sense and does not value the afterlife so highly that it is indifferent to annihilation. European officials believe that its recent behaviour — and even that since the 1979 revolution — suggests that it can be deterred.

The same cannot be assumed of militant groups with Iranian backing, if they got the bomb. If there is one residual benefit to the Litvinenko poisoning drama, and the looping trails of polonium-210 now detected across Europe, it may be in warning governments that they cannot hope to shuffle nuclear material into other hands without a high chance of being caught.

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