The US is planning further economic tightening on Iran, having imposed sanctions on Tehran since 1979.

US Treasury Secretary Scott Bessent will hold a press conference on Monday after vowing to implement "never-before-seen" measures against Iran.

And US President Donald Trump has threatened an "economic D-Day" against Iran.

The US has imposed sanctions on Iran since 1979, after the US embassy in Tehran was seized following the Iranian Revolution, according to the US State Department.

A Congressional Research Service (CRS) report on US sanctions on Iran says they were used to “deter, constrain, and encourage change in the Iranian regime’s hostile behavior.”

"US sanctions on Iran are perhaps the broadest and most comprehensive set of sanctions the United States maintains against any country," the report says.

The financial sanctions are broad, banning almost all U.S. trade with Iran, freezing Iranian government assets in the country, and prohibiting foreign aid and arms sales, the report describes.

In 2013, the Treasury Department's Office of Foreign Assets Control said the US could sell food, medicine, and medical equipment to Iran.

According to the CRS report, the US is also allowed to provide Iranians with telecommunications equipment to help them circumvent the Iranian regime's efforts to cut off internet access.