VIENNA - Pre-emptive military strikes aimed at forcing Iran to abandon its nuclear activities may end up having the opposite effect: convincing the Islamic Republic's leaders they need an atomic arsenal to secure their hold on power.That is the argument from those in the West and elsewhere who say the negative impact of an Israeli or US attack would eventually outweigh any gains - pushing Iran towards a decision that Western intelligence services believe it has not yet taken. "It is difficult to see a single action more likely to drive Iran into taking the final decision to acquire nuclear weapons than an attack on the country," the foreign ministers of Sweden and Finland said in an opinion piece in the New York Times. "And once such a decision was made, it would only be a matter of time before a nuclear-armed Iran became a reality," Carl Bildt and Erkki Tuomioja added.Israel says Iran's nuclear ambitions are a threat to the Jewish state's very existence and that time is running short to stop Tehran taking the irreversible step of acquiring the bomb.But an attack may delay Iran's nuclear drive only by a few years and would probably lead to an acceleration of the atomic program, the expulsion of UN inspectors and the Iranian people rallying around their leaders, the International Crisis Group think-tank said in a report citing unnamed US officials."Once UN inspectors are expelled, Iran could reconstitute its nuclear infrastructure, this time unambiguously geared to producing a bomb," ICG analyst Ali Vaez told Reuters.A similar message came from former CIA director Michael Hayden, who said the George W. Bush administration had concluded that a strike on the Islamic Republic's nuclear sites was a bad idea, according to a Foreign Policy magazine blog.An attack would guarantee the very thing that the West was trying to prevent - "an Iran that will spare nothing to build a nuclear weapon and that would build it in secret", Hayden was quoted as telling reporters and experts in January.Iran is relatively weak in conventional weaponry, compared to Israel and other Middle Eastern states, and may feel it has little choice but to develop nuclear bombs if "pushed into a corner," said military researcher Pieter Wezeman. He added that Iran wants to be seen as strong both internationally and within Iran.