The first set of US sanctions against Iran that had been eased under the landmark nuclear accord have gone back into effect under an executive order signed by President Donald Trump, targeting 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 Monday, 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."
Iranian President Hassan Rouhani said that Iran still can 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.
