Secretary of State Mike Pompeo has said the US is imposing the “strongest sanctions in history” on Iran.
In a speech in Washington, America’s top diplomat said Iran would be “battling to keep its economy alive” after the sanctions took effect.
He said he would work closely with the Pentagon and regional allies “to deter any Iranian aggression”.
Earlier this month, President Donald Trump took the US out of the landmark 2015 Iran nuclear deal.
In his first major foreign policy speech as secretary of state, Mr Pompeo unveiled the administration’s “Plan B” for countering the Islamic republic on Monday.
He laid out 12 conditions that Washington would need to be met for any “new deal” with Tehran, including pulling all its forces out of Syria and ending support for rebels in Yemen
America’s top diplomat said relief from sanctions would only come when Washington had seen a real change in Iran’s policies.
“We will apply unprecedented financial pressure on the Iranian regime,” he said.
“The leaders in Tehran will have no doubt about our seriousness.
“Iran will never again have carte blanche to dominate the Middle East.”
Following President Trump’s decision two weeks ago to withdraw the US from the Obama-era Iran nuclear deal, the US Treasury said economic sanctions would not be re-imposed on Tehran immediately, but would be subject to three-month and six-month wind-down periods.
His decision to pull out of the pact was roundly criticised by fellow signatories, including France, Germany, the UK and Russia.
Israel praised the Trump administration’s decision.
What was agreed under the 2015 deal?
The so-called Joint Comprehensive Plan of Action (JCPOA) saw Iran agree to limit the size of its stockpile of enriched uranium – which is used to make reactor fuel, but also nuclear weapons – for 15 years and the number of centrifuges installed to enrich uranium for 10 years.
Iran also agreed to modify a heavy water facility so it could not produce plutonium suitable for a bomb.
In return, sanctions imposed by the UN, US and EU that had crippled Iran’s economy were lifted.
The deal was agreed between Iran and the five permanent members of the UN Security Council – the US, UK, France, China and Russia – plus Germany.
Iran insists its nuclear programme is entirely peaceful, and its compliance with the deal has been verified by the International Atomic Energy Agency (IAEA).
US vows ‘strongest sanctions in history’ on Iran