US Treasury Department imposes sanctions on Iranian Foreign Minister Mohammed Javad Zarif.
The sanctions freeze any assets of Mr Zarif in America or are controlled by US structures, the Office said.
"Javad Zarif implements the reckless agenda of Iran's supreme leader (Ayatollah Ali Khamenei)," said Finance Minister Stephen Mnuchin.
Mr Zarif tweets that the US imposes sanctions on him because he considers it a threat to his agenda.
Tensions between the United States and Iran have intensified since last year the United States withdrew from a nuclear deal in 201
There is growing concern that a number of recent incidents in the Gulf may lead to a military conflict in a vital shipping area.
What did the US say?
Mr Mnuchin identified Mr Zarif as the main spokesman for the Iranian regime worldwide.
"The United States is sending a clear message to the Iranian regime that its recent behavior is completely unacceptable.
" At the same time, the Iranian regime denies Iranian citizens access to social media, Foreign Minister Javad Zarif spreads propaganda and misinformation to the regime's world through these mediums, "said Mr. Mnuchin.
Despite the sanctions, Mr. Zarif will still be able to travel to New York for official UN business, reports BBC News correspondent Gary Washington in Washington.
While there is a small pen The Washington-Tehran conversation spectrum, which is somewhat academic, is a matter for our negotiator, adds our correspondent.  How did Mr. Zarif respond?
Mr. Zarif said that the US move "had no effect on me." or my family as I have no property or interest outside of Iran. "
"The reason the US appoints me is that I am the main speaker of Iran all over the world. Is the truth really painful? "He asked.
" Thank you for considering me such a huge threat to your agenda. "
Well, the 2015 nuclear deal
Last year, the United States unilaterally withdrew from the agreement between Iran and the world powers.
Since then, Washington has restored severe sanctions affecting the Iranian economy and also
2015 deal – China, France, Germany, Russia and the United Kingdom criticized Mr Trump's decision and said they remain fully engaged in the deal.
Iran responded by violating the limit on its low-enriched uranium stockpile as part of a nuclear deal.
Tehran has stepped up production of enriched uranium used to produce reactor fuel, but also potentially nuclear bombs in May  Last week negotiations were held in Vienna to try to save the nuclear deal.  After meeting with representatives from the United Kingdom, France, Germany, Russia and China, a senior Iranian official said the atmosphere was "constructive".
What about the latest tanker incidents?
Tensions between Britain and Iran increased in July after British forces seized an Iranian tanker, Grace 1, off Gibraltar. It is said to be carrying oil in Syria in breach of EU sanctions, a claim rejected by Iran.
A few days later flag Stena Impero was detained by Iran, who said it "violated international maritime rules".
Britain sent a second warship on Sunday to escort its ships sailing through the Hormuz Strait. Recent incidents also include: