Iran’s President Hassan Rouhani has vowed to “break” swingeing sanctions re-imposed by the US targeting core parts of the economy.
The Trump administration is restoring all sanctions lifted under the 2015 nuclear deal in a bid to pressure Iran.
They will hit oil exports, shipping and banks, and make it difficult to do business with the oil-rich nation.
US Secretary of State Mike Pompeo said Iran must “act like a normal country, or see its economy crumble”.
He told a press conference on Monday that more than 20 nations have already cut their oil intake from the Islamic Republic, and that exports have fallen by a million barrels a day.
Mr Rouhani earlier struck a defiant tone, saying Iran would “continue selling oil”.