Donald Trump has warned countries doing business with Iran that they will not be doing business with the US.
Mr Trump also said in an early morning Twitter session that the sanctions placed back on Iran by the US were reintroduced in his pursuit for world peace.
The first set of US sanctions against Iran that had been eased under the landmark nuclear accord went back into effect early on Tuesday under an executive order signed by Mr Trump.
They targeted financial transactions that involve US dollars, Iran’s automotive sector, the purchase of commercial planes and metals including gold.
More US sanctions targeting Iran’s oil sector and central bank are to be reimposed in early November.
Mr Trump tweeted: “Anyone doing business with Iran will NOT be doing business with the United States.”
He added: “I am asking for WORLD PEACE, nothing less!”
The stiff economic sanctions ratchet up pressure on the Islamic Republic despite statements of deep dismay from European allies, three months after Mr Trump pulled the US out of the international accord limiting Iran’s nuclear activities.
Mr Trump declared the landmark 2015 agreement had been “horrible”, leaving the Iranian government flush with cash to fuel conflict in the Middle East.
Iran accused the US of reneging on the nuclear agreement, signed by the Obama administration, and of causing recent Iranian economic unrest. European allies said they “deeply regret” the US action.
As the sanctions loomed, Mr Trump said in a statement: “We urge all nations to take such steps to make clear that the Iranian regime faces a choice: either change its threatening, destabilising behaviour and reintegrate with the global economy, or continue down a path of economic isolation.”
Mr Trump warned that those who don’t wind down their economic ties to Iran “risk severe consequences”.
Despite Mr Trump’s claims, the accord “is working and delivering on its goal” of limiting Iran’s nuclear programme, said a statement by European Union foreign policy chief Federica Mogherini and the foreign ministers of France, Germany and the United Kingdom.
The ministers said the Iran deal is “crucial for the security of Europe, the region and the entire world”, and the European Union issued a “blocking statute” on Monday to protect European businesses from the impact of the sanctions.
A senior administration official, briefing reporters under ground rules requiring anonymity, said the United States is “not particularly concerned” by EU efforts to protect European firms from the sanctions.
Iranian President Hassan Rouhani said that Iran can still rely on China and Russia to keep its oil and banking sectors afloat. Speaking in a television interview, he also demanded compensation for decades of American “intervention” in the Islamic Republic.
Months of uncertainty surrounding the sanctions have already further hurt Iran’s economy. The country’s rial currency has tanked, and the downturn has sparked protests across the nation.
The “Trump Administration wants the world to believe it’s concerned about the Iranian people”, Iranian Foreign Minister Mohammad Javad Zarif said in a statement posted to Twitter. But, he said, the reimposed sanctions would endanger “ordinary Iranians”.
“US hypocrisy knows no bounds,” he said.
US officials insisted the American government stands with the people of Iran and supports many of their complaints against their own government.