The first set of US sanctions against Iran, that had been eased under the landmark nuclear accord, went back into effect today under an executive order signed by President Donald Trump.
The sanctions target financial transactions that involve US dollars, Iran's automotive sector, the purchase of commercial planes and metals including gold.
US sanctions targeting Iran's oil sector and central bank are to be reimposed in early November.
The stiff economic sanctions ratchet up pressure on the Islamic Republic despite statements of deep dismay from European allies, three months after Trump pulled the US out of the international accord limiting Iran's nuclear activities.
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 yesterday, 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."
Trump warned that those who don't wind down their economic ties to Iran "risk severe consequences."
The Europeans didn't like any of it.
Despite Trump's claims, the accord "is working and delivering on its goal" of limiting Iran's nuclear program, 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" today to protect European businesses from the impact of the sanctions.