The US has declared all international sanctions against Iran have been restored despite the rest of the world vowing to ignore the move.
Donald Trump's administration said on Saturday night its triggering of the so-called "snap back" mechanism in the UN Security Council resolution that enshrined the 2015 Iran nuclear deal had taken effect.
It comes 30 days after US Secretary of State Mike Pompeo notified the council Iran was in "significant non-performance" of its obligations under the deal.
The mechanism would mean that international sanctions eased or lifted under the nuclear deal are reimposed and must be enforced by UN member states.
However, other members of the council say Washington lost the legal ability to invoke it after the US withdrew from the nuclear deal and reimposed American sanctions on Iran.
In a statement, Pompeo said "the world will be safer as a result" of the US decision.
The White House plans to issue an executive order on Monday spelling out how it will will enforce the restored sanctions, with the State and Treasury departments expected to outline how foreign individuals and businesses will be penalised for violations.
Iranian Foreign Minister Mohammad Javad Zarif rejected the US move, saying the snapback mechanism and reimposed sanctions were invalid.
"This step is not supported by the UN Security Council because the US is no longer in the nuclear agreement and accordingly no longer plays a role in UN resolution 2231," Zarif said referring to the resolution in which the UNSC backed the Iran nuclear deal signed in Vienna in 2015.
The move by Washington was merely a "propaganda trick" before the US presidential election in November, Zarif said on Iranian state television.
Trump administration officials have been attacking the 2015 nuclear deal for years. They say it's fatally flawed because certain restrictions on Iran's nuclear activity gradually expire and will allow the country to eventually develop atomic weapons.
Washington's immediate concern has been the indefinite extension of the arms embargo that would otherwise expire on October 18. The Security Council rejected a US effort to extend the embargo in a lopsided vote which saw Washington get support from only one country, the Dominican Republic.
Australian Associated Press