The message comes the day after Donald Trump celebrated 100 days in the White House.
Foreign Minister Marco Rubio temporarily takes over the role of national security adviser in addition to his current tasks. Mike Waltz, who has a background in the military and as a congressman, gets a 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 outlets, citing sources.
Invited Editor-in-Chief
Trump's second term as president has so far been free from dramatic resignations. The Republican's first turn 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 come after the scandals surrounding the government's use of the messaging service Signal.
In March, The Atlantic magazine revealed that, among others, Mike Waltz, Defense Minister Pete Hegseth, Intelligence Chief Tulsi Gabbard, and Vice President JD Vance had discussed impending airstrikes against the Houthi movement on Signal. For unknown reasons, The Atlantic's editor-in-chief Jeffrey Goldberg had been invited to the chat group.
It was Waltz who started the chat and invited the participants.
Trump has consistently 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 resign. Hakeem Jeffries, minority leader in the House of Representatives, says more is to come.
Waltz is out. He's 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 with confidential information. According to the White House, no such information was shared in the Yemen chat – which contained details about aircraft types, drones, and times ahead of the US attacks on March 15.
