Iran has said a decision by the US to impose sanctions on the head of its judiciary has “Crossed a red line”.
The Foreign Ministry vowed to retaliate, but did not say what form such action might take.
Ayatollah Sadeq Amoli-Larijani was among 14 individuals and entities targeted over alleged rights abuses.
The US Treasury said Ayatollah Amoli-Larijani was responsible for the torture and degrading treatment of prisoners.
He was among those who had called for a crackdown following a recent spate of anti-government protests in Iranian cities.
It came as US President Donald Trump declared he would extend sanctions relief for Iran over its nuclear deal one last time.
He said he was giving Europe and the US “A last chance” to fix “terrible flaws” in the 2015 landmark agreement.
The White House wants EU signatories to agree permanent restrictions on Iran’s uranium enrichment. Under the current deal they are set to expire in 2025.
Iran on Saturday rejected any modification of its nuclear deal with world powers after us president Donald Trump demanded tough new measures to keep the agreement alive.
The Iranian Foreign Ministry said Tehran will not accept any amendments in Thed agreement, be it now or in the future.