Europe requests sanctions exemptions for businesses operating in Iran
"As allies, we expect that the United States will refrain from taking action to harm Europe's security interests," said the letter to US Treasury Secretary Steven Mnuchin and Secretary of State Mike Pompeo.
French Economy Minister Bruno Le Maire said the three countries and the EU were asking the US "to exempt European businesses doing legitimate trade in Iran from all extraterritorial American sanctions".
"Those businesses must be able to pursue their activities," he wrote on Twitter.
The request comes as European leaders ramp up their efforts to salvage the Iran nuclear deal after President Donald Trump announced in May the US would withdraw.
The 2015 accord was signed under Trump's predecessor Barack Obama.
Several major firms including France's Total have already said it will be impossible to continue doing business in the country once sanctions are fully reimposed unless they receive explicit exemptions.
But National Security Adviser John Bolton last month warned European businesses that they have just months to wind down their operations in Iran.
He specified at the time that companies would face immediate sanctions for new deals and have a maximum of six months to wind down current business activities in the country.
Iran's trade with the European Union is around 20 billion euros.
The country has the world's fourth-biggest oil reserves and second-biggest gas reserves in the world. The vast majority of EU purchases from Iran - 90 percent - is oil purchases, going primarily to Spain, France, Italy, Greece, the Netherlands and Germany.
The publication of Wednesday's letter came a day after Iran said it was preparing for the resumption of uranium enrichment within the limits set by the 2015 agreement. The modest steps appeared mainly aimed at signalling that Iran could resume its drive toward industrial-scale enrichment if the nuclear accord unravels.
The letter was also published during a trip to Europe by Israeli Prime Minister Binyamin Netanyahu, who has backed Trump in declaring the nuclear deal too soft on Iran.
Agencies contributed to this report.
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