The US Department of the Treasury has imposed sanctions against Iranian Foreign Minister Mohammad Javad Zarif.
“Javad Zarif implements the reckless agenda of Iran’s Supreme Leader (Ayatollah Ali Khamenei),” Treasury Secretary Steven Mnuchin said.
Mr Zarif tweeted the US had imposed sanctions on him because it considered him as a threat to its agenda.
Tensions between the US and Iran have heightened since the US last year withdrew from the 2015 nuclear deal that aimed to curb Iranian nuclear activities.
Iran has recently admitted breaching restrictions on its production of enriched uranium, used to make reactor fuel – but also potentially nuclear bombs.
There are also growing concerns that a number of recent incidents in the Gulf could lead to a military conflict in the vital shipping region.
What did the US say?
Mr Mnuchin described Mr Zarif as the Iranian “regime’s primary spokesperson around the world”.
“The United States is sending a clear message to the Iranian regime that its recent behaviour is completely unacceptable.
“At the same time the Iranian regime denies Iranian citizens’ access to social media, Foreign Minister Javad Zarif spreads the regime’s propaganda and disinformation around the world through these mediums,” Mr Mnuchin said.
Despite the sanctions, Mr Zarif will still be able to travel to New York on official UN business, the BBC’s Gary O’Donoghue in Washington reports.
And while there is little prospect of any talks between Washington and Tehran at the moment, the question of who to negotiate with is somewhat academic, our correspondent adds.
How did Mr Sharif respond?
Mr Zarif said the US move “has no effect on me or my family, as I have no property or interest outside of Iran”.
“The US reason for designating me is that I am Iran’s ‘primary spokesperson around the world. Is the truth really that painful?” he asked.
“Thank you for considering me such a huge threat to your agenda.”