US President Donald Trump has fired the Chairman of the Joint Chiefs of Staff CQ Brown, the highest-ranking officer in the country, as part of a major shake-up of top military leadership.

"I want to thank General Charles 'CQ' Brown for his over 40 years of service to our country," Trump posted on social media. He said five other top officers were also being replaced, BBC reported.

Gen. Brown was the second black officer to hold the post, the holder of which advises both the president and the secretary of defense on national security.

US Defense Secretary Pete Hegseth had previously said that Gen. Brown should be fired because of his "woke" focus on diversity, equity and inclusion programs in the military.

Later on Friday, Hegseth announced the firings of two additional senior officers: Chief of Naval Operations Admiral Lisa Franchetti and Vice Chief of Staff of the Air Force Gen. Jim Slife.

Franchetti was the first woman to lead the US Navy.

All three top officers removed on Friday were appointed by Trump's predecessor, Joe Biden.

Hegseth said in a statement: "Under President Trump, we are putting in place new leadership that will focus our military on its core mission of deterring, fighting and winning wars."

Trump said he would nominate Air Force Lt. Gen. Dan Caine - a career F-16 pilot who most recently served as CIA associate director for military affairs - as the new chairman of the joint chiefs of staff.

Last year, at the Conservative Political Action Conference, Trump recalled first meeting Gen. Caine in Iraq. "He looked better than any movie actor you could get," Trump told the audience.

In the same speech, he praised the military but said it was "woke at the top".

Gen. Brown had been visiting troops at the southern US border on Friday, roughly two hours before Trump's post announcing his departure.

Rumors had been swirling this week that the president would remove the commander, whose term was set to expire in 2027.

Gen Brown made headlines in 2020 when he spoke out about race following the death of George Floyd.