After the fallout of nearly every major nuclear agreement, New START is the last accord keeping the world from slipping back into a Cold War.
The embargo on the sale of arms to Iran was due to start expiring progressively from Sunday, under the terms of the UN resolution that blessed the 2015 nuclear deal between the Islamic republic and world powers.
Iran's President Hassan Rouhani says Washington's "maximum pressure" campaign against Tehran has thrown the US into "maximum isolation".
The UN envoys for Britain, France and Germany said that they remain committed to retain the nuclear agreement with Iran.
Washington will do everything it can to enforce UN sanctions on Iran if they are violated, says Secretary of State Mike Pompeo, following the US move to restore all UN sanctions on Iran.
The embargo on conventional arms is due to expire in mid-October, as agreed under the 2015 nuclear deal among Iran, Russia, China, Germany, Britain, France and the United States.
Iran's supreme leader has responded by ruling out negotiations with the US over Tehran's ballistic missile and nuclear programmes and urging Iranians to resist pressure.
With the main centres of power in Iran now firmly in the hands of the Revolutionary Guard, reconciliation with the US is near impossible.
The US has circulated a draft resolution to the 15-member council that would indefinitely extend the arms embargo on Tehran but Russia and China oppose the move.
"We deeply regret the US decision to end the three waivers covering key JCPOA nuclear projects in Iran," read a joint statement from Britain, France and Germany.
The US alleges Iran's satellite programme is a cover for its development of missiles, while the Islamic republic has previously insisted its aerospace activities comply with its international obligations.
Iran had previously committed to suspending operations at the plant as part of the Iran Nuclear Deal four years ago, but following Washington's abandonment of the deal, Iran has started abandoning its own commitments as well.
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