Tehran, June 25, 2019 (AFP) -

Iran said Tuesday US sanctions on its leaders represent the "permanent closure" of diplomacy with Washington, after President Donald Trump tightened the screws on a nation he has threatened with "obliteration".

"Imposing fruitless sanctions against Iran's supreme leader and the commander of Iran's diplomacy is the permanent closure of the path to diplomacy with Trump's desperate government," ministry spokesman Abbas Mousavi said in a tweet.

Washington imposed new sanctions against supreme leader Ayatollah Ali Khamenei Monday ahead of blacklisting Foreign Minister Mohammad Javad Zarif later this week, its latest salvo in a tense standoff that has raised fears of a regional conflict.

"Trump's government is destroying all established international mechanisms for keeping global peace and security," he added.

Tehran and Washington broke off diplomatic relations in 1980 over the hostage crisis at the US embassy in Tehran following Iran's Islamic revolution.

US President Donald Trump also imposed new sanctions Monday against top Iranian military chiefs, pressuring the country it has threatened with "obliteration" if a war breaks out.

The US Treasury said it plans to blacklist Iran's Foreign Minister Mohammad Javad Zarif -- a moderate figure and key architect of the 2015 Iran nuclear deal -- and eight top commanders from Iran's Revolutionary Guards.

Trump called the punitive measures "a strong and proportionate response to Iran's increasingly provocative actions."

A year after Trump unilaterally withdrew from a multilateral pact with Iran over its nuclear programme, tensions have flared with a series of attacks on tankers in highly sensitive Gulf waters.

Washington blamed the incidents on Iran, accusations Tehran vehemently denies.

Tensions rose further last week as Iran shot down a US spy drone last week.

Trump then ordered a retaliatory strike on Iran but said he had called it off at the last minute.