A senior Iranian official said on Friday there was no difference between the outgoing and incoming US special envoys for Iran because American officials "bite off more than they can chew".
US Secretary of State Mike Pompeo announced Thursday that the top US envoy for Iran, Brian Hook, was leaving his post and the US special representative for Venezuela, Elliott Abrams, would add Iran to his role.
Hook's surprise departure comes at a critical time when Washington has been intensely lobbying at the United Nations to extend an arms embargo on Iran and as the UN Security Council prepares to hold a vote on the US resolution next week.
Pompeo did not give a reason for the change but wrote in a tweet that Hook was moving on to the private sector.
"There's no difference between John Bolton, Brian Hook or Elliott Abrams," Iranian Foreign Ministry spokesman Abbas Mousavi said in a tweet under the hashtag #BankruptUSPolicy.
"When US policy concerns Iran, American officials have been biting off more than they can chew. This applies to Mike Pompeo, Donald Trump and their successors," Mousavi added.
President Donald Trump last year fired his national security adviser John Bolton, a veteran hardliner on Iran who advocated military action to destroy Tehran's nuclear programme.
Hook, 52, was named to the top Iran role at the State Department in late 2018 and has been instrumental in the Trump administration's "maximum pressure" campaign against Tehran since Trump pulled Washington out of world powers' 2015 nuclear deal with the Islamic Republic.
Abrams, 72, a Republican foreign policy veteran, was named US special representative for Venezuela in January 2019 and has led a hawkish approach aimed at removing Venezuelan President Nicolas Maduro.