Trump's withdrawal from a landmark 2015 nuclear agreement in May had already spooked investors and triggered a run on the Iranian rial long before nuclear-related sanctions went back into force.
Iran is also taking solace in the fact that most of the world strongly opposes Trump's policy, with China, India and Turkey all saying they are unwilling to substantially cut purchases from Iran when the United States reimposes sanctions on the energy sector on November 5.
Heavier US sanctions, aimed at Iran's oil sector, are due in November.
They also unveiled a "blocking statute" which is meant to protect European firms doing business with Iran despite the new USA sanctions.
The European Investment Bank (EIB) would risk its business model if it invested in Iran, because of the sanctions the USA reinstated after its withdrawal from the nuclear deal, the president of the EIB told the press on Wednesday (18 July).
Iran accused the USA of reneging on the nuclear agreement, signed by Barack Obama's administration, and of causing recent Iranian economic unrest.
"We deeply regret the re-imposition of sanctions by the U.S", the European Union said in a statement.
The two other signatories to the 2015 pact - Russian Federation and China - also continue to support it.
"There is a clear interest around the world", one staffer said.
The impact of the return of sanctions has ramped up tension inside Iran, which has seen days of protests and strikes in multiple towns and cities over water shortages, high prices and wider anger at the political system.
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Looming US sanctions against Iran will likely hit Tehran's oil sales overseas, and it could lead to a price spike in oil contracts.
He said Iran's leaders may need to "drink the poison cup" and negotiate with the US. It also blocks the effect of any USA court actions in Europe related to the sanctions.
The United States continues to stand with the long-suffering Iranian people, who are the rightful heirs to Iran's rich heritage and the real victims of the regime's policies, indicated the statement.
"They've got to behave like a normal country".
"We want to put unprecedented pressure on the government of Iran to change its behavior, and so far they've shown no indication they're prepared to do that".
"If you're an enemy and you stab the other person with a knife, and then you say you want negotiations, then the first thing you have to do is remove the knife", he told state television.
"If Iran were really serious they'd come to the table".
Many large European firms are leaving Iran for fear of United States penalties, and Mr Trump warned of "severe consequences" against firms and individuals that continued to do business with Iran.
Among large European companies that have suspended ambitious plans to invest in Iran in response to Trump's sanctions are France's oil major Total and its big carmakers PSA and Renault.