WASHINGTON: Major companies, particularly in Europe, could see billions of dollars in commercial deals canceled because of the US decision to reinstall sanctions on Iran, though the ultimate impact remains unclear due to the possibility of renegotiations and exemptions, experts say. President Donald Trump's decision to withdraw from the Iran nuclear deal and re-impose sanctions on Iran means companies worldwide must stop doing business with the country or run afoul 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 sector and type of products sanctioned. And firms would not be able to generate new business. Certain exemptions and waivers can be negotiated, but the US did not say what goods 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 U.S. 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 unacceptable, he added, though it was unclear still how European leaders would respond. Among US companies, plane maker Boeing has signed the biggest deals, and U.S. Treasury Secretary Steven Mnuchin said Tuesday that its existing licenses — 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 airplanes for around $19 billion at list prices. Boeing later struck its own deal with IranAir for 80 aircraft with a list price of some $17 billion, promising that deliveries would begin in 2017 and run until 2025. Boeing separately struck another 30-airplane deal with Iran's Aseman Airlines for $3 billion at list prices. 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 license because it makes at least 10 percent of its aircraft components in the US, says 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. In the case of oil sales, there will be a 180-day period for countries to wrap up existing contracts and achieve 'significant reductions' in their purchases of crude from Iran. Mnuchin did not spell out what the administration would consider as a 'significant reduction' in purchases of oil. US law gives the Treasury secretary the power to administer sanctions imposed by the president. So far, French oil company Total SA has been the most aggressive Western oil company to move back into Iran, signing in July a $5 billion, 20-year agreement there. A Chinese oil company also has a deal to develop the country's massive South Pars offshore natural gas field. Total did not respond to requests for comment.