Joe Biden, flanked by Secretary of State Antony Blinken and Secretary of Defence Lloyd Austin, makes a statement to the news media ahead of a cabinet meeting at the White House in Washington. File / Reuters

Austin, who sits just below Biden at the top of the chain of command of the US military, withheld his multi-day hospitalization, which started on New Year's Day, from the president and the public for several days.

"There is no plan for anything other than for Secretary Austin to stay in the job," John Kirby, the National Security Council spokesman, told reporters.

Former President Donald Trump, who is Biden's likely Republican challenger in the 2024 election, said on Sunday night that Austin should be fired for his "improper professional conduct and dereliction of duty."

"He has been missing for one week, and nobody, including his boss, Crooked Joe Biden, had a clue as to where he was, or might be," Trump wrote on Truth Social.

Another prominent Republican in Congress also called for Austin's resignation Monday.

"There must be full accountability beginning with the immediate resignation of Secretary Austin and those that lied for him and a Congressional investigation into this dangerous dereliction of duty," Elise Stefanik, a New York representative and House Republican Conference chair said in a statement.

Asked whether Austin had been unconscious at all since Jan. 1, and whether the White House had been informed about that, a White House official, speaking on condition of anonymity, said he did not know.

Officials disclosed on Sunday that Austin's hospitalization was kept far more secret than previously known, adding his deputy to a long list of people right up to Biden who were kept in the dark for days.

Austin's duties require him to be available at a moment's notice to respond to any national security crisis. He said on Saturday that he took "full responsibility" for the secrecy over his hospitalization.

What health issue spurred Austin's hospitalization is unknown. Kirby said he did not have that information, but that Biden and Austin had talked in recent days.

Reuters