US President Donald Trump has said he is imposing hard-hitting new sanctions on Iran, including on the office of the country's Supreme Leader Ali Khamenei.
Trump said the additional sanctions were in response to the shooting down of a US drone and "many other things".
Ayatollah Khamenei, Iran's highest authority, was singled out because he was "ultimately responsible for the hostile conduct of the regime".
Iranian Foreign Minister Javad Zarif said the Americans "despise diplomacy".
In a tweet sent after the announcement, Zarif also accused the Trump administration of having a "thirst for war".
Tensions between the two countries have been escalating in recent weeks.
However, US Treasury Secretary Steve Mnuchin said Trump's executive order - which would lock up "billions" of dollars in Iranian assets - was in the works before Tehran shot down an unmanned US drone in the Gulf last week.
The UN Security has urged calm and the use of diplomacy.
The US Treasury department said eight senior Iranian commanders who "sit atop a bureaucracy that supervises the IRGC's [the elite Islamic Revolution Guard Corps] malicious regional activities", were being targeted.
It added that Trump's executive order would also "deny Iran's leadership access to financial resources and authorises the targeting of persons appointed to certain official or other positions by the Supreme Leader or the Supreme Leader's Office", as well as foreign financial institutions which help them conduct transitions.
Sanctions will also be imposed on Zarif later this week, according to Mnuchin.
Putting sanctions on the Ayatollah Ali Khamenei is significant. He is indeed the Supreme Leader, with the ultimate say in Iran's politics and military - and he has enormous economic power.
He supervises an organisation known as Setad, which confiscated property abandoned after the 1979 revolution and morphed into a business juggernaut with holdings of about $95bn (£75bn).
Setad was already under US sanctions, but President Trump has gone further, targeting anyone connected to the Ayatollah - presumably including those sitting on company boards, or officials in his extensive "shadow government".
BDST: 0914 HRS, JUNE 25, 2019