The White House was unaware for days that Defense Secretary Lloyd Austin had been hospitalized, at least one official told US media, the BBC reports.

Austin, 70, was hospitalized Monday due to complications from surgery, the nature of which was not disclosed.

An official told CBS that the White House had not been informed of this until at least Thursday morning.

Austin took responsibility for the lack of communication.

“I recognize that I could have done a better job of ensuring the public was properly informed,” he said in a statement, adding: “I am committed to doing better.”

Mr Austin added: “It is important to say that this was my medical procedure and I take full responsibility for my decisions regarding disclosure.”

“I’m very happy to be in good shape and look forward to returning to the Pentagon soon.”

He is believed to be still in hospital, but a defense ministry spokesman, quoted by the French news agency, said he had returned to duty on Friday.

As the BBC notes, it is not clear how much of his responsibilities Austin was able to carry out because of his illness, nor the extent to which Deputy Defense Secretary Kathleen Hicks stepped in to help.

Officials told CNN that she had taken over his duties periodically during his hospital stay while she was in Puerto Rico on vacation.

Meanwhile, Joe Biden reportedly had a “heated” conversation with Mr Austin on Saturday.

“The president has full confidence in Secretary Austin. He is looking forward to returning to the Pentagon,” an official told AFP.

Republicans are among those who have expressed serious concern about the situation. “The Secretary of Defense is the key link in the chain of command between the president and the military, including the nuclear chain of command, when the toughest decisions have to be made in minutes,” said Senator Tom Cotton.

“If this report is true, there should be consequences for this shocking collapse,” he said.

Senator Roger Wicker said that while he was glad to hear of Mr Austin’s recovery, “the fact remains that the Department of Defense willfully concealed the defense secretary’s medical condition for days. This is unacceptable”.

The Pentagon Press Association, made up of journalists covering the Defense Department, criticized the lack of coverage in a letter to the Pentagon on Friday.

Mr. Austin, a retired general, became the first African-American defense secretary in 2020.