US President Donald Trump has announced new sanctions against Iran after Tehran threatened to enrich its stockpile of uranium.

The US president has issued an executive order imposing new restrictions on Iranian steel, aluminium, copper and iron, which account for 10 per cent of Tehran's total exports, reported Emirates news agency Wam.

Trump said Tehran could expect "further actions unless it fundamentally alters its conduct."

"Today's action targets Iran's revenue from the export of industrial metals - 10% of its export economy - and puts other nations on notice that allowing Iranian steel and other metals into your ports will no longer be tolerated," he said in a statement.