The United States will reimpose what it calls the toughest sanctions regime ever imposed on Iran.
The sanctions are due to take effect on November 5.
The measures target Iran's energy, shipping and banking sectors.
The U-S Secretary of State Mike Pompeo has set out 12 demands that Iran must meet in order to have the sanctions lifted.
They include that Iran must end support for terrorism and military intervention in Syria and halt nuclear and ballistic missile development.
Mr Pompeo says it's a necessary step.
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