Swift, the body that handles global banking transactions, says it will cut Iran’s banks out of the system on Saturday to enforce sanctions.
The move will isolate Iran financially by making it almost impossible for money to flow in and out of the country via official banking channels.
It will hit its oil industry, but may also have a heavy impact on Iranians who live abroad and send money home.
The move follows EU sanctions against Iran over its nuclear programme.
The US and its allies accuse Iran of trying to develop nuclear weapons – a charge it denies.
This is just wrong