In response, Iran agreed to sign on to an agreement allowing more intrusive inspections of its nuclear sites by UN inspections.
"The draft resolution has just been adopted by consensus," Mark Gwozdecky told reporters shortly after the 35-nation board of directors of the International Atomic Energy Agency (IAEA) opened a meeting.
The text, adopted minutes after the IAEA meeting opened in Vienna Wednesday, balances the US call to condemn Iran for 18 years of hidden nuclear activities that included making plutonium and Britain, France and Germany's demand that Iran be rewarded for cooperating since October with the IAEA.
Iran said Wednesday it was ready to sign an accord on wider, snap inspections of its nuclear sites by the atomic agency despite the tough resolution.
"Certainly we have committed ourselves to signing the additional protocol (to the nuclear Non-Proliferation Treaty - NPT) and that's what we're going to do," Ali Akbar Salehi, Iran's ambassador to the IAEA, told reporters.
He said Iran accepted the resolution even though it "would have preferred a better text."
But Salehi added that Iran is "appreciative of this collaborative effort of the international community."
After days of negotiations, the United States bowed to European demands for a softer approach to Tehran to prevent the Islamic republic from breaking off all cooperation with the UN nuclear watchdog agency.
US Secretary of State Colin Powell said Tuesday that he was "very satisfied" with the resolution from Europe's big three which he said had sufficient teeth to punish any future Iranian violations of non-proliferation safeguards.
Non-proliferation expert Gary Samore told AFP the resolution was "a good compromise given that the United States, which says Iran is covertly developing nuclear weapons, was never going to get "backing at the IAEA board to take Iran to the UN Security Council, which could impose sanctions.
The United States "had to find a compromise that kept the pressure on Iran. I think this does," said Samore, a former US official now at the International Institute for Strategic Studies think tank in London.
"Basically, the board has given Iran another four months to demonstrate it can carry out commitments," Samore said, referring to the next IAEA board meeting in March.
In Paris, European Union foreign policy representative Javier Solana said he was "very happy" with what he saw as EU efforts to curb the development of nuclear weapons in Iran through diplomacy.
The IAEA board had been considering how to respond to a report from its chief Mohamed ElBaradei that Tehran has violated nuclear safeguards for the past 18 years, including making small amounts of plutonium and enriched uranium.
But ElBaradei said there was so far no evidence Iran was working on making nuclear weapons, an assertion Washington, which says Iran is part of an "axis of evil" along with North Korea and Saddam-era Iraq, derided as "simply impossible to believe."
The United States dropped demands to take Iran immediately before the Security Council for "non-compliance" with the NPT but insisted that the resolution contain a so-called trigger mechanism stating that "any further Iranian failures come to light, the Board of Governors would meet immediately to consider . . . all options at its disposal."
Diplomats said the three European states had feared that a direct mention of the Security Council could cause Iran to pull back from its October 21 agreement with them to cooperate with the IAEA.
That pact has led to Iran filing a comprehensive report on its nuclear program, pledging to allow wider inspections and suspending the enrichment of uranium.
In return, Iran was promised the issue would not go to the Security Council.