White House Chief of Staff John Kelly stands before a Medal of Honor ceremony in the East Room of the White House in Washington, US, July 31, 2017. [Photo/Agencies]

WASHINGTON - John Kelly was sworn in as US President Donald Trump's new Chief of Staff on Monday, amid a series of staff shake-ups in the White House.

As a retired four-star Marine Corps general, Kelly had served as homeland security secretary since late January before Trump announced his appointment as the White House Chief of Staff on Friday.

At a swearing-in ceremony in the Oval office on Monday, Trump praised Kelly for "record-shattering" performance in heading the Department of Homeland Security (DHS).

Kelly, 67, has taken a hard line against illegal immigration. His execution of a controversial travel ban signed by Trump on several Muslim countries was repeatedly praised by the president.

While congratulating Kelly on "a fantastic job" serving the DHS, Trump said he expected the former US Southern Command leader to do a "better job" at the helm of the White House.

Kelly's arrival at the West Wing comes amid a string of shake-ups in a chaotic White House.

Press Secretary Sean Spicer resigned on July 21 to protest against Trump's appointment of wealthy New York financier Anthony Scaramucci as White House communications director.

Within days of his controversial naming, Scaramucci started accusing Kelly's predecessor, Reince Priebus, of leaking damaging information about him to the media, and later launched a vulgar tirade against Priebus and chief White House strategist Steve Bannon.

Priebus, who was blamed for failing to keep the White House in order and push forward the GOP legislative agenda, resigned after being caught in the feud, while Scaramucci was removed from his position on Monday after Trump felt the financier's remarks against Priebus and Bannon "inappropriate."

Though it is unclear whether Trump or Kelly had decided to remove Scaramucci, White House Press Secretary Sarah Huckabee Sanders said in a press conference on Monday afternoon that Kelly would have "full authority to carry out businesses he sees fit" to bring "new structure, discipline and strength to the White House."