Donald Trump has warned Tehran that he will order severe military action against Iran if it assassinates a US diplomat in retaliation for the American killing of a top Iranian general.

The US president issued the dramatic warning a day after the news site Politico reported Iran was considering killing Lana Marks, the American ambassador to South Africa. Politico said any Iranian move would be retaliation for the US assassination in January of Qassem Soleimani, who was Iran’s most powerful military commander. The report was not confirmed by other major US news organisations.

In a late-night tweet, Trump said that “according to press reports Iran may be planning an assassination, or other attack, against the United States in retaliation for the killing of terrorist leader Soleimani”.

He added: “Any attack by Iran, in any form, against the United States will be met with an attack on Iran that will be 1,000 times greater in magnitude!”

Ali Rabiei, Iran’s government spokesman, dismissed Trump’s threat as “propaganda”. He warned the US leader against making a “strategic mistake” and said Iran would respond if he did