Trump says he is replacing Kristi Noem as Homeland Security Secretary

Kristi Noem is being replaced as US Homeland Security Secretary, Donald Trump said (J Scott Applewhite/AP)

US president Donald Trump has said he is replacing his embattled Homeland Security Secretary Kristi Noem and will nominate in her place Oklahoma Republican Senator Markwayne Mullin.

Mr Trump made the announcement on social media on Thursday, two days after Ms Noem faced a grilling on Capitol Hill from Republican members as well as Democrats.

Mr Trump said he will make Ms Noem a “special envoy for The Shield of the Americas”, a new security initiative that he said would focus on the Western Hemisphere.

Ms Noem is the first Cabinet secretary to leave during Mr Trump’s second term.

Her departure caps a tumultuous tenure overseeing immigration enforcement tactics that have been met with protests and lawsuits.