The US unleashed its “toughest ever” sanctions against Iran on Monday, a move that has already sparked mass protests in the oil-rich nation.
The Trump administration reinstated all sanctions removed under the 2015 nuclear deal, targeting both Iran and states that trade with it.
They will hit oil exports, shipping and banks – all core parts of the economy.
Thousands of Iranians chanting “Death to America” rallied on Sunday, rejecting calls for talks.
Iranian President Hassan Rouhani has vowed to sell oil and break the sanctions.
The military was also quoted as saying it would hold air defence drills on Monday and Tuesday to prove the country’s capabilities.
The demonstrations took place on the 39th anniversary of the occupation of the US embassy in Tehran, which led to four decades of mutual hostility.
Before travelling to a campaign rally for the US mid-term elections, President Donald Trump said Iran was already struggling under his administration’s policies.
He called the sanctions, “very strong”, saying: “We’ll see what happens with Iran, but they’re not doing very well, I can tell you.