Since the sanctions were lifted in 2016, major European companies, partly wary of the remaining US sanctions on Iran, have been reluctant to do business with Tehran, which needs to attract over $100 billion in foreign investment to boost its crude output.
Major companies, particularly in Europe, could see billions of dollars in commercial deals cancelled 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.
The same can not be said of the biggest risk factor by far; Iran may turn its back on the global community completely and redouble efforts to develop its nuclear industry. We have the support of the Arab oil-producing monarchies and many others. It meant most owners weren't able to haul Iranian oil and forced some Asian buyers of the Middle East country's crude to find awkward workarounds such as state-backed cover.
"In the short to medium term, I do not envisage a fall in Iranian exports to below one million barrels a day".
White House National Security adviser John Bolton said USA sanctions on European companies that maintain business dealings with Iran were "possible".
After the President threatened foreign firms that continue trading with Iran with "strong sanctions", Trump's national security adviser John Bolton told American TV he thought the United Kingdom and France would follow suit and ditch the 2015 deal.
"However, if they resist the pressure from America, then I expect to see a small number of refineries being targeted by the United States treasury - imposing heavy fines on them to make an example for other refineries".
And Russian President Vladimir Putin has spoken to German Chancellor Angela Merkel and Turkey's President Recep Erdogan about how to save the 2015 agreement with Iran, according to Russia's official press agency TASS.
The deal between Iran and six world powers lifted most worldwide sanctions in 2016 in return for Tehran curbing its nuclear programme, under strict surveillance by the United Nations, to stockpile enriched uranium for a possible atomic bomb. I think it was testing the limits of the deal's provisions, exceeding them in some cases.
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On 8 May President Donald Trump denounced the deal, saying he would withdraw the USA from it.
Iran signed the nuclear deal in 2015 with the United States, as well as Britain, China, France, Germany and Russian Federation.
"We could have pushed the Europeans a lot harder, to work with us, " Gates said on "Face the Nation".
"My forecast is that should Europe cave in under pressure and boycott Iranian oil, Iran will see a reduction of 700,000 barrels a day in its exports", he added.
US President Donald Trump on May 8 announced that the United States was withdrawing from the 2015 deal negotiated by the Obama administration.
In their opening remarks, Lavrov said Russia, Iran and the other signatories of the deal, including China and three European countries, should together "defend their legitimate interest stipulated by this agreement".
As those sanctions kick in, it will have an even broader effect as well, Bolton said.
"We will be instituting the highest level of economic sanctions".
"We are closely monitoring developments following (the) USA administration decision. and will assess our position and commercial arrangements accordingly", Hellenic said.
Germany said it would spend the next few months trying to persuade Washington to change its mind.
Germany's minister for economic affairs Peter Altmaier said last week that Berlin will try to "persuade the U.S. government to change its behaviour".