WASHINGTON -- US President Donald Trump announced Thursday that he will replace Homeland Security Secretary Kristi Noem amid growing bipartisan frustration with Noem's leadership.

"I am pleased to announce that the Highly Respected United States Senator from the Great State of Oklahoma, Markwayne Mullin, will become the United States Secretary of Homeland Security (DHS), effective March 31, 2026," Trump said on Truth Social.

"The current Secretary, Kristi Noem, who has served us well, and has had numerous and spectacular results ... will be moving to be Special Envoy for The Shield of the Americas, our new Security Initiative in the Western Hemisphere we are announcing on Saturday in Doral, Florida. I thank Kristi for her service at 'Homeland,'" he said.

The announcement, the first Cabinet shakeup since Trump's second term, came shortly after US media reported that the president was considering firing Noem, who has been under bipartisan pressure after federal law enforcement officers fatally shot two US citizens in Minneapolis.

Trump, already frustrated with Noem, "was incensed" by her performance this week during congressional hearings and was considering firing her, NBC News quoted lawmakers and people familiar with the discussions as saying.

"The final straw for Trump was Noem's combative hearing Tuesday before the Senate Judiciary Committee, which showed bipartisan frustration with Noem's leadership, the advisers said," according to a report by The Wall Street Journal.

"Noem's decision to allot 200 million dollars for an ad campaign, featuring herself urging those living illegally in the US to self-deport, had already rankled the president for months for its self-promotional style," the report said.

Noem has been facing mounting pressure in recent weeks following the fatal shootings of two US citizens in Minneapolis. On Jan 7, an Immigration and Customs Enforcement officer shot and killed 37-year-old US citizen Renee Good. On Jan 24, Border Patrol officers fatally shot 37-year-old US citizen Alex Pretti.

The backlash has focused on Noem's comments describing the victims as having committed "an act of domestic terrorism," a claim not supported by video evidence.

The secretary of the US Department of Homeland Security must be confirmed by the Senate, in which Republicans hold a majority.