Last Monday, the chief United Nations nuclear inspector gathered ambassadors and experts from dozens of nations in a boardroom high above the Danube in Vienna and laid out a trove of evidence that he said raised new questions about whether Iran had tried to design an atom bomb.

For more than two hours, representatives to the International Atomic Energy Agency (IAEA) were riveted by documents, sketches and even a video that appeared to have come from Iran’s own military laboratories. The inspector said they showed work “not consistent with any application other than the development of a nuclear weapon,” according to notes taken by diplomats.

The presentation caught no one’s attention more than the Iranian representatives in the room, who deny Iran is developing atomic weapons. As they whipped out cellphone cameras to photograph the screen, Iran’s ambassador, Ali Asghar Soltanieh, nearly shouting, called the evidence baseless fabrications, the diplomats said, and warned that the agency was going down “a very dangerous road.”

Suddenly, the confrontation with Iran had reignited.

The display of new and newly declassified information is part of the latest effort to pressure Iran to disclose information about its past atomic activities and offer proof that its current program is benign. France’s ambassador, François-Xavier Deniau, said questions raised by the Vienna meeting had opened a “new chapter” in the West’s effort to keep Iran from acquiring nuclear arms, according to participants.

This confrontation is different from the long-running American-led campaign. Gone are the veiled threats of military action from the White House. The wind largely went out of that effort in December, when American intelligence officials surprised Western allies — and angered Bush administration hawks— with a report saying Iran had halted its nuclear weapons program in 2003. Last Monday’s presentation in Vienna did not contradict that conclusion, but disclosed many new details suggesting the depth of Iran’s past work on weapons design.

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