U.S. President Joe Biden has no plans to sack Defense Secretary Lloyd Austin after he came under fire for failing to disclose his hospitalization for days, but his administration will investigate the "lack of transparency," a White House official said Monday.

White House national security spokesman John Kirby said Biden wants to keep working with Austin, as the president respects "the amazing job" he has done as Pentagon chief and very much values his advice and leadership.

"The president's number one focus is on (Austin's) health and recovery, and he looks forward to having him back at the Pentagon as soon as possible," Kirby told reporters aboard Air Force One. "There is no plan for anything other than for Secretary Austin to stay in the job."

The remarks came as Republican lawmakers and former President Donald Trump, Biden's potential opponent in the November presidential election, called for Austin's removal for not promptly informing the White House and top Pentagon officials of his hospitalization.

U.S. Defense Secretary Lloyd Austin (R) is pictured at the Pentagon in December 2023, in Arlington, Virginia. (Getty/Kyodo)

Austin, 70, was admitted into intensive care at Walter Reed Army Medical Center on New Year's Day, but Biden and his aides were not made aware until three days later.

The Pentagon did not inform the public until Friday, and the reason for his hospitalization has not been divulged.

On concerns about transparency, Austin said in a statement the following day, "I recognize I could have done a better job ensuring the public was appropriately informed. I commit to doing better. But this is important to say: this was my medical procedure, and I take full responsibility for my decisions about disclosure."

On Monday, Defense Department spokesman Pat Ryder told reporters that Austin remains hospitalized at the medical center but is "recovering well" and his "prognosis is good."

Ryder said Austin initially underwent an elective medical procedure at the facility on Dec. 22, adding he was discharged the following day and continued to work from home through the holidays.

Ryder said Austin began experiencing severe pain on the evening of Jan. 1 and was transported by ambulance to the facility.

He also said Deputy Defense Secretary Kathleen Hicks did not know the reason for the transfer of authority to her until Thursday.

Kirby and Ryder said officials are reviewing whether Austin and the Pentagon handled the matter appropriately.

"We'll take a look at the process and procedure here and try to learn from this experience," Kirby said.

Ryder said a delay in notifying the appropriate people was caused partly by Austin's chief of staff being out sick with the flu.

While it remains unclear when Austin will be released from the medical center at a time of numerous security challenges, including Russia's invasion of Ukraine and the war between Israel and the Palestinian militant group Hamas, Ryder said the secretary is focused on his duties.

Ryder said Austin has monitored the Pentagon's day-to-day operations worldwide since resuming his duties on Friday evening and has given necessary guidance to senior staff.

He added Austin spoke Monday with Hicks and Biden's top national security aide Jake Sullivan in separate phone calls.