The Trump administration is to reinstate all US sanctions on Iran removed under the 2015 nuclear deal in a "maximum pressure" effort to cripple the country's economy.
US officials said Friday they were determined to force Tehran to give up its nuclear activities and what the US says is broad support for "terrorism" in the region, reimposing severe economic penalties six months after President Donald Trump's administration quit the 2015 Iran nuclear deal.
There will also be sanctions to cut off Tehran's ability to export oil, the country's most crucial foreign exchange earner, though US Secretary of State Mike Pompeo said eight importers would be given exemptions in exchange for slowing their purchases -- a bid to avoid upsetting the global crude market.
The reimposition of sanctions "is aimed at depriving the regime of the revenues it uses to spread death and destruction around the world," Pompeo said.
"Our ultimate aim is to compel Iran to permanently abandon its well-documented outlaw activities and behave as a normal country."
When Trump withdrew from the nuclear deal struck between world powers and Iran, he began reimposing sanctions that had been suspended or removed by his predecessor Barack Obama.
That process will be completed starting from midnight Sunday, US eastern time, when sanctions on the regime's banks, shippers, shipbuilders and oil sector are imposed.
The impact remains in question as other countries, particularly Washington's European allies, are resisting joining its effort to economically strangle the Tehran regime.
Britain, France, Germany and the European Union strongly condemned the US move, as they did when Washington withdrew in May from the Iran nuclear deal, the Joint Comprehensive Plan of Action.
"The JCPOA is a key element of the global nuclear non-proliferation architecture and of multilateral diplomacy," they said.
"It is crucial for the security of Europe, the region, and the entire world. The JCPOA is working and delivering on its goal."
Pompeo said the US would grant exemptions to eight countries that have pledged to or have already cut back on purchases of petroleum from Iran, which has long depended on crude exports to power its economy.
He did not name the eight countries, but they are believed to include India, Japan, South Korea, and possibly China.
Iran's northern neighbor Turkey said it was one of the eight.
"We know Turkey is among the countries that will be given an exemption but we do not have the details," Energy Minister Fatih Donmez said, according to state-run news agency Anadolu.
Pompeo said the countries agreed that the payments for the oil would go into escrow accounts that Iran will only be able to tap for "humanitarian trade, or bilateral trade in non-sanctioned goods and services."
"Maximum pressure means maximum pressure," Pompeo said.
To punish Iranian banks, US Treasury Secretary Steve Mnuchin said SWIFT -- which enables secure bank-to-bank communications and transactions -- will also face sanctions if it provides services to blacklisted Iranian financial institutions.
The US blacklist includes most major Iranian banks.
That could make it extremely difficult for Iran to do business with other countries.
"SWIFT is no different than any other entity," Mnuchin said.
The US wants the Shia clerical regime to withdraw from war-ravaged Syria, where it is a critical ally of President Bashar al-Assad, and to end longstanding support to regional militant movements Hezbollah and Hamas.
It also wants Iran to stop backing Yemen's Huthi rebels, who are facing a US-supported air campaign led by Saudi Arabia.
"It's important to keep our eyes on the prize when it comes to Iranian revenues, whether they be derived from oil or any other sort of sanctionable transaction. The goal is to target and tie up these revenues to change Iran's calculus," said Behnam Ben Taleblu of the Foundation for Defense of Democracies.
"SWIFT now must make a choice," he said: refuse to deal with Iran banks on the US blacklist, or face sanctions itself.
But experts don't expect Iran's leaders to immediately throw in the towel.
"It's basically magical thinking," said Ali Vaez of the International Crisis Group.
"The Iranians have been able to continue their support to regional proxies and allies for 40 years despite economic pressure."