After days of diplomacy, Russia and China have agreed to support a US-backed resolution demanding that Iran stop activities that could be used to make nuclear arms.
Diplomats said on Wednesday the agreement sent a unified message to Iran, but also convinced Israel that diplomacy was a real alternative to military force in preventing a nuclear confrontation.
The resolution cannot be enforced by the 35-nation board of the International Atomic Energy Agency (IAEA), even if approved by vote or consensus as expected on Thursday. But with Israel threatening war against Iran, the agreement is a significant progress after months of diplomatic deadlock.
Israel views a nuclear-armed Iran as a strategic threat, citing Iran's persistent calls for the destruction of the Jewish state, its development of missiles capable of striking Israel, and Iranian support for Arab armed groups.
Iran insists its nuclear programme is for peaceful purposes only.
But it refuses foreign offers of reactor fuel if it stops making its own through uranium enrichment - a process that worries the international community because it could also be used to arm nuclear warheads.
Concerns also focus on nuclear watchdog's suspicions that Iran has worked secretly on nuclear arms - allegations Iran dismisses as based on fabricated US and Israeli intelligence.
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The new resolution singles out Iran's defiance of UN Security Council resolutions to suspend uranium enrichment, its refusal to allow IAEA inspectors into the Parchin military base and the suspected removal of evidence of nuclear weapons research.
According to a draft seen by AFP, it stresses "once again its serious concern that Iran continues to defy the requirements and obligations contained in the relevant IAEA Board of Governors and UN Security Council Resolutions".
It is significant that Western nations were able to get Moscow and Beijing on board as they are traditionally more lenient on Tehran, with China a major buyer of Iranian oil and Russia having close commercial ties with Iran.
The draft resolution comes as the European Union is considering imposing more sanctions on the Islamic republic.
The timing is also important since it follows weeks of growing speculation that Israel may bomb the Gulf country's atomic facilities, said Mark Hibbs, analyst at the Carnegie Endowment for International Peace.
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," Hibbs 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 closer to "break-out capacity".
In particular, Binyamin Netanyahu, the Israeli prime minister, has been pressing US President Barack Obama to identify "red lines" for when it would take action.
"The world tells Israel: Wait, there's still time. And I say: wait for what? Wait until when?" Netanyahu said on Tuesday in comments clearly aimed at the White House.
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 late on Tuesday night.
The IAEA's latest report on August 30 said Iran had doubled since May the capacity at the underground Fordo site by installing about 1,000 new centrifuges, although the number of machines operational was unchanged.
Enriched uranium can be used for nuclear power generation or medical purposes but also, when highly purified, in the fissile core of an atomic bomb.