India, March 6 -- US President Donald Trump abruptly fired Homeland Security Secretary Kristi Noem on Thursday, removing one of the most visible figures in his administration's immigration crackdown and triggering the first cabinet-level shake-up of his second presidential term.

Trump announced the decision on social media, saying he would nominate Republican Senator Markwayne Mullin of Oklahoma to lead the Department of Homeland Security, pending Senate confirmation. The move followed days of political turmoil surrounding Noem's leadership, including a contentious congressional hearing and mounting criticism over controversial enforcement actions and spending decisions.

The firing ends a turbulent tenure for Noem, the former South Dako...