Major companies, particularly in Europe, could see billions of dollars in commercial deals cancelled because of the US decision to reinstall sanctions on Iran.
President Donald Trump's decision to withdraw from the Iran nuclear deal and reimpose sanctions on Iran means companies worldwide must stop doing business with the country or run foul of the US government.
Companies and countries with commercial deals with Iran would have either 90 or 180 days to wind down those activities, depending on the type of products being sanctioned.
Certain exemptions and waivers can be negotiated, but the US did not say what products or countries might qualify.
Since the Iran nuclear deal was struck in 2015, it was mainly European companies that moved back in to strike deals with Iran, making Trump's decision particularly painful for the region.
"US Iran sanctions are hardly hitting any US companies, but aim primarily at European ones," Carl Bildt, the former leader of Sweden who is now co-chair of the European Council on Foreign Relations, said in a tweet.
The EU has in the past found this utterly unacceptable, he added.
Among US companies, plane maker Boeing has signed the biggest deals, and US Treasury Secretary Steven Mnuchin said Tuesday that its existing licences - as well as those of its European competitor, Airbus Group - would be invalidated.
In December 2016, Airbus signed a deal with Iran's national carrier, IranAir, to sell it 100 planes for around $US19 billion. Boeing later struck its own deal with IranAir for 80 aircraft with a list price of some $US17 billion. Boeing separately struck another 30-airplane deal with Iran's Aseman Airlines for $US3 billion.
Boeing has yet to deliver any aircraft to Iran under those deals and said that it will "continue to follow the US government's lead."
Airbus, which is subject to the US licence because it makes at least 10 per cent of its aircraft components in the US, said it will abide by the new US sanctions but it could take "some time" to determine the full impact on the industry. It has already delivered two A330-200s and one A321 to Iran.
The US says the sanctions will also sharply curtail sales of oil by Iran, which is currently the world's fifth-largest oil producer.
So far, French oil company Total SA has been the most aggressive Western oil company to move back into Iran, signing in July a $US5 billion, 20-year agreement with Iran.
In other sectors, French carmaker PSA Peugeot Citroen reached a deal in 2016 to open a plant producing 200,000 vehicles annually in Iran. It said Wednesday that it is studying the implications of the US move and hopes the European Union will have a united position on the Iranian sanctions.
A group representing German trade interests said the US decision to withdraw from the Iran nuclear deal will hit German companies and urged the EU to protect their interests. Trade between Germany and Iran reached 3.4 billion euros last year.
Mnuchin said the US goal is to impose tough sanctions that will prompt Iran to renegotiate the Iran nuclear deal.
"These sanctions do impact all the major industries (in Iran). They are very strong sanctions," Mnuchin said. "They worked last time. That is why Iran came to the table."
