The UN Security Council on Friday rejected a last-minute effort backed by Russia and China to delay for six months the reimposition of sanctions on Iran.
The vote on a draft resolution failed to secure the minimum nine votes needed in the 15-member Security Council.
As a result, all UN sanctions on Iran suspended under a 2015 nuclear agreement will automatically “snap back” into effect on Sunday.
Nine members voted against, four in favour, and two abstained from voting.
The measures will freeze Iranian assets abroad, ban arms sales to Tehran and curb development of its ballistic missile programme, further straining an economy already weakened by years of restrictions.
Britain, France and Germany triggered the 30-day mechanism last month, accusing Tehran of breaching the 2015 nuclear deal aimed at curbing its atomic programme.
The European powers argue Iran has advanced uranium enrichment activities well beyond levels necessary for civilian use, eroding the milestone agreement.
The Russian and Chinese-sponsored draft would have delayed the sanctions and urged all parties to “immediately resume negotiations” to return to the table.
“Iran undertook all possible measures to accommodate the E3 [UK, France and Germany] and the US. Did Washington, London, Paris, Berlin, make new compromises? No, they did not,” Russian deputy ambassador Dmitry Polyanskiy told Council members.
European nations have said they would be willing to extend the deadline if Iran complies with a series of conditions.
These include resumption of direct negotiations with the US over Tehran's nuclear programme, allowing UN nuclear inspectors access to its nuclear sites, and accounts for the more than 400 kilograms of highly enriched uranium the UN watchdog says it has.
France disagreed with Russia and described efforts it made throughout this week's General Assembly to reach an agreement with Iran on a proposal of extension.
“We sought an immediate agreement, yet Iran preferred to postpone everything,” said Jerome Bonnafont, France’s UN envoy.
Deputy US envoy Dorothy Shea said Washington was “pleased” that China's and Russia's “last-ditch effort” had failed.
“The snapback of these measures does not preclude removal through diplomacy, but at this stage there is no basis for changing course,” she added.
Britain, France and Germany say Iran has flouted restrictions that would ensure it never develops an atom bomb – such as limits on its uranium stockpile.
Iran – which insists its intentions are peaceful – agreed to those terms in 2015 in exchange for many sanctions being lifted, notably on its oil and banking sectors.
“The failure of high-level engagement between senior Iranian and European diplomats … underscores the difficulty in getting Tehran and Washington back to negotiations after the June war,” said the International Crisis Group’s Iran project director Ali Vaez on Friday.
He added that while western diplomats expect difficulties in implementation, the revived measures “will add a multilateral layer to the unilateral US ‘maximum pressure’ campaign against the Islamic Republic.”
Conflict over Iran's nuclear activities led to a 12-day air war with Israel in June, which culminated in a US bombing of Iran and an Iranian strike against an airbase in Qatar used by American forces.
Iran’s Foreign Minister Abbas Araghchi told the Security Council that the US and its European allies bore full responsibility for the fallout from their decision to restore sanctions.
"The developments we have witnessed set a dangerous precedent," he said. "If agreements can be broken at will, no nation can trust international commitments. If unlawful measures are enforced by power instead of law, the Secretary Council risks losing credibility and authority. Such a situation would harm not only Iran, but the entire system of international law and collective security."
