US Defense Secretary Lloyd Austin's undisclosed hospitalization and cancer diagnosis have triggered a congressional inquiry.

President Joe Biden did not learn that his defense secretary, Lloyd Austin, had prostate cancer until Tuesday, the White House said.

"Nobody at the White House knew that Secretary Austin had prostate cancer until this morning," John Kirby, the National Security Council spokesman, said at a press conference. "And the president was informed immediately after."

US Representative Mike Rogers, chairman of the House Armed Services Committee, launched a formal inquiry into Austin's "failure to disclose his hospitalization and incapacitation."

What do we know about Austin's health condition?

The 70-year-old Austin was diagnosed in early December, doctors said, after a regular screening. He "underwent a minimally invasive surgical procedure" and went home the next day.

He then underwent surgery to treat the cancer on December 22, developing an infection a week later.

On January 1, Austin reported nausea and severe abdominal, hip and leg pain due to the infection, doctors said, adding that he had developed a urinary tract infection.

Doctors report the cancer was detected early and that his prognosis is excellent.

The Pentagon waited until Friday evening to announce that Austin, 70, had been hospitalized at the Walter Reed military hospital in the Washington suburbs four days prior.

Questions about accountability

Biden said on Monday he did not plan to fire Austin after the defense chief failed to disclose a hospital stay.

Austin and Biden spoke on Saturday, and it was unclear why the president did not learn until Tuesday about Austin's prostate cancer.

Republicans seized on the incident as evidence of dereliction of duty by Austin.

"With wars in Ukraine and Israel, the idea that the White House and even your own Deputy did not understand the nature of your condition is patently unacceptable," Rogers wrote in a letter to Austin on Tuesday.

The congressman also wrote to Austin's deputy Kathleen Hicks and his Chief of Staff Kelly Magsamen, seeking information and full transparency on what took place during the hospitalization.

Some of Austin's authorities were transferred to Hicks. Hicks, who was in Puerto Rico at the time, was not told the reason for the transfer of authorities until January 4.

Austin has no plans to quit Deutsche Welle

Typically, high-ranking cabinet officials report planned medical absences ahead of time.

The apparent breach of protocol comes at a time when the US is embroiled in a crisis in the Middle East.

Republicans and some Democrats have called for Austin to resign or be sacked.

The US defense chief took responsibility for the delays in notification, in a statement on Saturday evening.

"I recognize I could have done a better job ensuring the public was appropriately informed. I commit to doing better," he said.

On Tuesday Major General Patrick Ryder, Pentagon press secretary, said, "The secretary continues to remain focused on recovering but more importantly, on carrying out his duties as secretary of defense and defending the nation."