US President Donald Trump fired top US military officer General Charles "CQ" Brown on Friday, as part of a major shake-up of the armed forces' leadership.

Trump offered no explanation for Brown's dismissal less than two years into his four-year term as chairman of the Joint Chiefs of Staff, which followed sweeping layoffs of federal workers and moves to dismantle government institutions just a month into the president's second term.

Brown had been nominated to the top military role by Democratic president Joe Biden and became only the second Black person to hold the position.

Following Trump's announcement on Brown, Defense Secretary Pete Hegseth said he was seeking a replacement for Admiral Lisa Franchetti, the first woman to serve as the top US Navy officer.

Trump thanked Brown for "his over 40 years of service to our country" in a post on his Truth Social platform, describing him as "a fine gentleman and an outstanding leader."

The decision sets off a period of upheaval at the Pentagon, which is already bracing for firings of civilian staff, a dramatic overhaul of its budget and a shift in U.S. military deployments under Trump's new America First foreign policy. (Agencies)