The U.S. State Department has said Brian Hook, the U.S. government's pointman on Iran policy under President Donald Trump, has resigned.
Secretary of State Mike Pompeo said in a statement August 6 that Elliott Abrams, another diplomat who has led the Trump administration's push to topple Venezuela's leadership, would take his place temporarily.
Hook did not give a reason for leaving.
His departure comes as the United Nations Security Council prepares for a vote on a U.S. push to extend an international arms embargo on Iran.
Hook became the U.S. special envoy for Iran policy in August 2018, not long after the Trump administration announced it would withdraw from the 2015 international nuclear accord that lifted crippling sanctions on Iran in exchange for Tehran agreeing to curb its nuclear ambitions.
Since then, the Trump administration has steadily ramped up its pressure and rhetoric against Tehran.
Despite severe economic problems, Iran's leadership has so far refused to budge or give in to U.S. pressure.
Abrams, who will be taking over from Hook, was a key figure in the 2003 Iraq war.
He will take on the Iran portfolio as he continues his work seeking to topple Venezuelan President Nicolas Maduro, Pompeo said.