The announcement followed several media reports earlier in the day that Mike Waltz was being squeezed out of the National Security Council, along with his deputy, Alex Wong, a China specialist.
The move was seen as a major early shake-up in the White House following the start of the president’s second term some 100 days ago.
“I am pleased to announce that I will be nominating Mike Waltz to be the next United States Ambassador to the United Nations,” Trump wrote on social media. “In the interim, Secretary of State Marco Rubio will serve as National Security Advisor, while continuing his strong leadership at the State Department.”
Waltz’s transfer follows a scandal that broke last month after Jeffrey Goldberg, editor of The Atlantic magazine, was mistakenly added to a chat among US government officials on the secure platform Signal. Waltz has been blamed for adding Goldberg to the group.

Trump has sought to avoid the turnover churn seen during his first term, and analysts said the reassignment may be meant to save face and remove Waltz without the negative publicity associated with an outright sacking.