When US President Barack Obama stood last week with the leaders of Britain and France to denounce Iran's construction of a secret nuclear plant, the Western powers all appeared to be on the same page.

Behind their show of unity about Iran's clandestine efforts to manufacture nuclear fuel, however, is a continuing debate among US, European and Israeli spies about a separate component of Iran's nuclear program: Its clandestine efforts to design a nuclear warhead.

The Israelis, who have delivered veiled threats of a military strike, say they believe that Iran has restarted these “weaponisation” efforts, which would mark a final step in building a nuclear weapon. The Germans say they believe that the weapons work was never halted. The French have strongly suggested that independent international inspectors have more information about the weapons work than they have made public.

Meanwhile, in closed-door discussions, US spy agencies have stood firm in their conclusion that while Iran may ultimately want a bomb, the country halted work on weapons design in 2003 and probably has not restarted that effort — a judgment first made public in a 2007 National Intelligence Estimate.

The debate, in essence, is a mirror image of the intelligence dispute on the eve of the Iraq war.

This time, US spy agencies are delivering more cautious assessments about Iran's clandestine programs than their Western European counterparts.

The differing views colour how each country perceives the imminence of the Iranian threat and how to deal with it in the coming months, including this week's negotiations in Geneva -- the first direct talks between the United States and Iran in more than 30 years.

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