US President Donald Trump announced he has fired Brian Hook, the special envoy for Iran during his previous term, as he marked his return to the White House on Monday.

"Our first day in the White House is not over yet! My Presidential Personnel Office is actively identifying and removing over a thousand presidential appointees from the previous administration who are not aligned with our vision to Make America Great Again," Trump wrote in a post on Truth Social shortly after midnight.

He added, "Brian Hook from the Wilson Center for Scholars… YOU'RE FIRED!"

It was not clear which position Hook was being fired from because he was also involved in managing Trump's hiring for the state department.

During Trump’s previous presidency, Hook played a key role in championing the administration's heavy sanctions, which targeted Iran's economy and strained the Islamic Republic’s finances.