The US on Monday unleashed its "toughest ever" sanctions against Iran, a move that has already sparked mass protests in the oil-rich nation.
US President Donald Trump’s administration reinstated all sanctions removed under the 2015 nuclear deal, targeting both Iran and states that trade with it.
More than 700 individuals, entities, vessels and aircraft were now on the sanctions list, including major banks, oil exporters and shipping companies.
Washington has also said that it wanted to stop what it calls Tehran’s "malign" activities including cyber attacks, ballistic missile tests, and support for terror groups and militias in the Middle East.
The Trump administration has granted exemptions to eight countries to continue importing Iranian oil, without naming them. They are reported to include US allies India, Italy, Japan and South Korea.
Iranian President Hassan Rouhani has vowed to sell his country’s oil and break the sanctions.
Iran’s military has said that it would hold air defence drills on Monday and Tuesday to prove the country’s capabilities.
Before travelling to a campaign rally for the US midterm elections, President Trump said Iran was already struggling under his administration’s policies.
"The Iran sanctions are very strong. They are the strongest sanctions we’ve ever imposed. And we’ll see what happens with Iran, but they’re not doing very well, I can tell you."
The UK, Germany and France – which are among the five countries still committed to the nuclear pact – have all objected to the sanctions, the BBC said.
They have promised to support European firms that do "legitimate business" with Iran and have set up an alternative payment mechanism – or Special Purpose Vehicle (SPV) – that will help companies trade without facing US penalties.
On Sunday, thousands of Iranians chanting "Death to America" rallied, rejecting calls for talks.
The rallies coincided with the siege of the US embassy on November 4, 1979 , which took place soon after the fall of the US-backed shah.
Some 52 Americans were held hostage in the embassy for 444 days and the two countries have been enemies ever since.>