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 President Donald Trump.

The US sanctions target financial transactions that involve US dollars, Iran’s automotive sector, the purchase of commercial planes and metals including gold.

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 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 on Monday, 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 do not wind down their economic ties to Iran “risk severe consequences”.

Despite 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 UK.

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 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 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.

Iran Sanctions
Iranian president Hassan Rouhani struck a hard line as the US restored some sanctions that had been lifted under the 2015 nuclear deal (Iranian Presidency Office via AP)

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.

National security adviser John Bolton said Iran’s leadership is on “very shaky ground,” but he insisted economic pressure from the Trump administration is not an attempt at “regime change”.

Secretary of State Mike Pompeo said sanctions are an important pillar in US policy toward Iran and will remain in place until the Iranian government radically changes course.

“They’ve got to behave like a normal country. That’s the ask. It’s pretty simple,” said Mr Pompeo, en route on Sunday from a three-nation trip to Southeast Asia.

Israeli prime minister Benjamin Netanyahu, a firm foe of the Iranian government, said the sanctions symbolise “the determination to block Iran’s regional aggression as well as its continuous plans to arm itself with nuclear weapons”.

He called on the countries of Europe to join the US, saying, “The time has come to stop talking; the time has come to do.”

The US has long designated Iran as the world’s foremost state sponsor of terrorism, Mr Pompeo noted on Sunday, adding that the Islamic Republic cannot expect to be treated as an equal in the international community until it halts such activities.

He said that “there’s no evidence today of a change in their behaviour,” and in the meantime “we’re going to enforce the sanctions.”