Noem has been criticized, among other things, for her controversial efforts targeting irregular migrants in the United States and for an appearance before the House Judiciary Committee earlier this week.
Trump announced the firing of Noem on Truth Social on Thursday, following speculation that the controversial official would be replaced.
His replacement will be Senator Markwayne Mullin of Oklahoma.
"The current Secretary, Kristi Noem, has served us well. She has achieved several spectacular results (especially on the border!)," Trump writes, explaining that she will be the U.S. special envoy for the "America's Shield" initiative for the Western Hemisphere.
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