The first set of U.S. sanctions against Iran that had been eased under the landmark nuclear accord went back into effect early Tuesday under an executive order signed by President Donald Trump, targeting financial transactions that involve U.S. dollars, Iran's automotive sector, the purchase of commercial planes and metals including gold.

More U.S sanctions targeting Iran's oil sector and central bank are to be reimposed in early November.

In an early-morning tweet, Trump said the re-imposition of sanctions mean, "Anyone doing business with Iran will NOT be doing business with the United States."

"I am asking for WORLD PEACE, nothing less!"

Donald Trump tweet

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 U.S. 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 U.S. 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 U.S. 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, destabilizing behavior 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" 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 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.

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.

U.S. 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 U.S. 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 Pompeo, en route Sunday from a three-nation trip to Southeast Asia.

Israeli Prime Minister Benjamin Netanyahu, a firm foe of the Iranian government, said the sanctions symbolize "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 U.S., saying, "The time has come to stop talking; the time has come to do."

The U.S has long designated Iran as the world's foremost state sponsor of terrorism, Pompeo noted 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 behavior," and in the meantime "we're going to enforce the sanctions."