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.

'Reckless actions'

Meanwhile, Iran on Sunday called on the rest of the world to unite against the "reckless actions" of the US.

“We expect the international community and all the countries in the world to stand against these reckless actions by the regime in the White House and speak in one voice,” foreign ministry spokesman Saeed Khatibzadeh told a news conference in Tehran.

“The whole world is saying nothing has changed,” Khatibzadeh said, adding sanctions were in place only in the “imaginary world” of US Secretary of State Mike Pompeo.

“This is much ado about nothing, and I believe these are the most bitter days and hours for the United States,” he added.

Calling Washington “isolated” and “on the wrong side of history”, Khatibzadeh said Tehran's message for it was to “return to the international community, to your commitments, stop rebelling and the world will accept you.”

'Consequences'

Pompeo had promised in his announcement that measures would be announced in the coming days against “violators” of the sanctions.

“If UN member states fail to fulfill their obligations to implement these sanctions, the United States is prepared to use our domestic authorities to impose consequences for those failures and ensure that Iran does not reap the benefits of UN-prohibited activity,” he stated.

With 45 days to go until the November 3 election, Trump could unveil those measures in his speech at the UN General Assembly on Tuesday.

In mid-August, US suffered a resounding defeat at the UN Security Council when it tried to extend the embargo on conventional weapons being sent to Tehran, which was due to expire in October.

Pompeo made an unusually vehement attack on France, Britain and Germany, accusing them of “siding with Iran's ayatollahs,” and on August 20 announced the snapback.

The Trump administration, however, is acting as if the international sanctions are in place, while the rest of the international community continues to act as if nothing has changed.

Washington is hammering home that the arms embargo has been extended “indefinitely” and that many activities related to Tehran's nuclear and ballistic missile programs are now subject to international sanctions.

Some observers said Washington's latest announcement was counterproductive.

“I don't see anything happening,” said one UN diplomat. “It would be just a statement. It's like pulling a trigger and no bullet coming out.”

Another diplomat deplored the “unilateral” US act, saying that “Russia and China are sitting, happy, eating popcorn, watching” the “huge destabilising fallout” between Washington and its European partners.

Russia's deputy ambassador to the UN, Dmitry Polyanskiy, lamented the decision.

“It's very painful to see how a great country humiliates itself like this, opposes in its obstinate delirium other members of UN Security Council,” he tweeted.

“We all clearly said in August that US claims to trigger #snapback are illegitimate. Is Washington deaf?” But if the US were to carry out the threat of secondary sanctions, tensions could continue to spiral.