The first set of US 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 US dollars, Irans automotive sector, the purchase of commercial planes and metals including gold. More US sanctions targeting Irans oil sector and central bank are to be reimposed in early November. In an early-morning tweet, Trump said "The Iran sanctions have officially been cast. These are the most biting sanctions ever imposed, and in November they ratchet up to yet another level." "Anyone doing business with Iran will NOT be doing business with the United States. I am asking for WORLD PEACE, nothing less." The stiff economic sanctions ratchet up pressure on the Islamic Republic, three months after Trump pulled the US out of the international accord limiting Irans 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. Trumps contempt for the nuclear deal dates back to his time as presidential candidate and on May 8, he made good on a pledge to pull America out of the international agreement. The unilateral withdrawal came despite other parties to the agreement pleading with Trump not to abandon the pact aimed at blocking Iran from acquiring a nuclear weapon. Iran accused the US of reneging on the nuclear agreement, signed by the Obama administration, and of causing recent Iranian economic unrest. 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 dont wind down their economic ties to Iran "risk severe consequences." 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 Irans economy. The countrys rial currency has tanked, and the downturn has sparked protests across the nation. 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 Irans 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. "Theyve got to behave like a normal country. Thats the ask. Its pretty simple," said Pompeo, en route Sunday from a three-nation trip to Southeast Asia. The US has long designated Iran as the worlds foremost state sponsor of terrorism, Pompeo noted Sunday, adding that it cannot expect to be treated as an equal in the international community until it halts such activities. He said that "theres no evidence today of a change in their behavior," and in the meantime "were going to enforce the sanctions."