The United States unilaterally proclaimed on Saturday that United Nations sanctions against Iran were back in force and promised to punish those who violate them, in a move other major countries — including its allies — said lacked legal basis.
The so-called snapback — announced last month — also drew a sharp rebuke from Tehran, which called on the rest of the world to unite against US "reckless actions".
“Today, the United States welcomes the return of virtually all previously terminated UN sanctions on the Islamic Republic of Iran,” Secretary of State Mike Pompeo said in a statement.
He said the measures were back in effect from 8pm Washington time (0000 GMT Sunday).
The Trump administration also promised to “impose consequences” on any UN member state which does not comply with the measures.
The sanctions in question were lifted in 2015 when Iran signed on to an international agreement not to seek to build nuclear weapons.
But President Donald Trump withdrew the US from the landmark accord in 2018, saying the deal — negotiated by his predecessor Barack Obama — was insufficient. He then renewed and even strengthened Washington's own sanctions.
At the moment, the US is insisting it is still a participant in the agreement that it stormed out of, but only so it can activate the snapback option, which it announced on August 20.
Virtually every other member of the Security Council disputes Washington's ability to execute this legal pirouette, and the council has not taken the measure any further.
On Sunday, two permanent council members — France and Britain — issued a joint statement along with non-permanent member Germany saying Pompeo's “purported notification” was “incapable of having any legal effect".
Russia's foreign ministry also said in a statement that Washington's statements lacked legal authority.
“The illegitimate initiatives and actions of the United States by definition cannot have international legal consequences for other countries,” it said.