The message comes after Trump has just celebrated 100 days in the White House.
Foreign Minister Marco Rubio temporarily takes over the role alongside his current tasks. Mike Waltz, who has a background in the military and as a congressman, is nominated for the new job.
"I am pleased to announce that I will nominate Mike Waltz to become the US Ambassador to the United Nations. From his time in uniform on the battlefield, in Congress, and as my national security adviser, Mike Waltz has worked hard to put our nation's interests first. I know he will do the same in his new role," Trump writes on Truth Social.
Even the Deputy Security Adviser Alex Wong will leave, reports several American media, citing sources.
In contrast to when Waltz was appointed, the ambassador role must be approved by the Senate.
"I am deeply honored to continue serving President Trump and our fantastic nation," Waltz writes in a post on X.
Invited editor-in-chief
Trump's second term has so far been free from dramatic resignations. The Republican's first stint in the White House was tumultuous, with, for example, four different national security advisers, four chiefs of staff, and two foreign ministers, writes AP.
The departures now occur after the scandals surrounding the Trump administration's use of the messaging service Signal.
The Atlantic magazine revealed in March that, among others, Mike Waltz, Defense Minister Pete Hegseth, Intelligence Chief Tulsi Gabbard, and Vice President JD Vance discussed an impending air strike against the Houthi movement in Yemen on the messaging service. For unknown reasons, The Atlantic's editor-in-chief Jeffrey Goldberg had been invited to the group chat. It was Waltz who was responsible for the chat.
Trump has publicly expressed support for Waltz and called him "a good man" who "has learned his lesson", notes CBS News.
More to come
Several high-ranking Democrats have demanded that both Waltz and Hegseth to resign. Now, Hakeem Jeffries, minority leader in the House of Representatives, says more is to come.
Waltz is out. He is the first. He will certainly not be the last, he says to Fox News.
Earlier, a number of high-ranking officials at the Defense Department have been fired.
Signal is an encrypted service, but not approved for use for classified information. According to the White House, no such information was shared in the Yemen chat – which contained details about aircraft types, drones, and times for the US attacks on March 15.
