The UN atomic agency's board approved with a crushing majority Thursday a resolution criticising Iran brought by world powers that was also aimed at dissuading Israel from military action.
The resolution expresses "serious concern that Iran continues to defy" UN Security Council resolutions for it to suspend uranium enrichment, a process which can be used for peaceful purposes but also in a nuclear weapon.
It also highlights the International Atomic Energy Agency's complaint that activities at the Parchin base near Tehran, where it suspects nuclear weapons research took place, would "significantly hamper" inspectors -- should Iran let them visit.
The resolution was introduced at the meeting of the IAEA's 35-nation board of governors on Wednesday after days of haggling between Western nations and Russia and China, which are seen as more lenient on Tehran.
It was approved by 31 countries, with Cuba voting against and Egypt, Ecuador and Tunisia abstaining, all four of them members of the Non-Aligned Movement of which Iran is currently the rotating president.
Another NAM member, South Africa, had introduced an amendment on a minor change of wording that resulted in several hours' delay. The last resolution in November saw Cuba and Ecuador vote against and Indonesia abstain.
Iran insists its expanding atomic programme is for peaceful purposes, but since the IAEA has repeatedly said that it is unable to vouch for this, the UN Security Council has passed six resolutions against Tehran, four with sanctions attached.
The United States and the European Union have also imposed additional unilateral sanctions that have hit Iran's vital oil exports hard, and EU foreign ministers said last weekend they are considering additional measures.
"I think this resolution sends a very clear signal to Iran that the diplomatic pressure is intensifying and Iran's isolation is growing," US envoy to the IAEA Robert Wood told reporters in Vienna after the vote.
"The time right now is for compliance over defiance and Iran needs to comply now with its obligations.... We hope that Iran will hear and understand the message and begin to cooperate with the agency."
"We are determined, with those countries that are ready, to further increase sanctions against Iran, as long as it continues to refuse to comply with its international obligations," French foreign ministry spokesman Vincent Floreani said in a statement.
Iran's envoy Ali Asghar Soltanieh hit back saying the resolution "is not the way to resolve the Iranian nuclear issue.
"It will only complicate the situation and jeopardise the cooperative environment," Soltanieh told journalists.
"More than ever there is a need for reform of the decision-making process of the board of governors... It was designed 50 years ago. It doesn't cope with the reality of today."
The IAEA resolution, the 12th in nine years, stopped short of referring Iran to the Security Council.
But it was significant that Western nations were able to get Moscow and Beijing on board, and at a time of heightened speculation that Israel, the Middle East's sole if undeclared nuclear-armed state, might bomb Iran, analysts say.
The resolution "reflects the desire of member states to underscore that diplomacy is paramount and it warns Israel in two separate paragraphs that the diplomatic process should be supported," Mark Hibbs from the Carnegie Endowment for International Peace told AFP.
Israeli frustration has grown at what it sees as a failure by the international community to take seriously the threat posed by Iran or to stop it inching ever closer to "break-out capacity".
In particular, Israeli Prime Minister Benjamin Netanyahu has been pressing US President Barack Obama to identify "red lines" for when it would take action.
Obama, running for re-election in November and keen to avoid being depicted as soft on Iran by Republican challenger Mitt Romney, spoke to Netanyahu for an hour by phone earlier this week.