In the first Cabinet shuffle of his second term, President Donald Trump on Thursday announced he's nominating Michael Waltz to be U.S. ambassador to the United Nations, while Secretary of State Marco Rubio will serve as interim national security adviser while keeping his current role as well.

Axar.az reports, ABC News, "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 his conservative social media platform. "From his time in uniform on the battlefield, in Congress and, as my National Security Advisor, Mike Waltz has worked hard to put our Nation's Interests first. I know he will do the same in his new role."

"In the interim, Secretary of State Marco Rubio will serve as National Security Advisor, while continuing his strong leadership at the State Department," Trump continued. "Together, we will continue to fight tirelessly to Make America, and the World, SAFE AGAIN. Thank you for your attention to this matter!"

Sources had told ABC News earlier Thursday that Waltz was expected to leave his post as national security adviser.

The move came as President Trump has been increasingly frustrated by Waltz after he came under intense scrutiny for inadvertently adding a reporter to a Signal chat with top Trump officials discussing a U.S. military strike on Houthi rebels in Yemen.

Waltz responded to Trump's announcement on X, writing: "I'm deeply honored to continue my service to President Trump and our great nation."

U.N. ambassador nominees require Senate approval and Waltz would need to face what could be uncomfortable questions at confirmation hearings.