Officials at Walter Reed National Military Medical Center announced Tuesday that Secretary Austin has been hospitalized since January 1 as the result of complications from surgery to treat prostate cancer.

The announcement comes after a week of Department of Defense officials refusing to give details on why Mr. Austin was hospitalized. At a press briefing on Tuesday, Major General Pat Ryder said that the secretary resumed his duties Friday evening from the hospital room.

“Secretary Austin has taken responsibility for the issues with transparency, and the department is taking immediate steps to improve our notification procedures,” General Ryder said.

Pentagon officials did not tell the White House that Mr. Austin had been hospitalized for three days after he was first admitted. At a White House press conference on Tuesday, the assistant to the secretary of defense for public affairs, John Kirby, said that President Biden only learned of Mr. Austin’s cancer diagnosis Tuesday morning.

Medical professionals treating Mr. Austin previously described the surgery that Mr. Austin underwent as “elective.” General Ryder was not able to elaborate on the discrepancy.

The initial prostatectomy was performed on December 22. Mr. Austin was readmitted on January 1 for treatment of symptoms, including “nausea with severe abdominal, hip, and leg pain.” His condition was diagnosed as a urinary tract infection. During his second stay in the hospital, Mr. Austin has never lost consciousness, according to the hospital press release.

General Ryder added that Mr. Austin’s chief of staff instructed defense department officials to conduct a “30-day review of the department’s notification process for assumption of functions and duties of the secretary of defense.”

Mr. Austin transferred some of his authority to a deputy secretary between January 1 and January 5; while on vacation in Puerto Rico, the deputy executed some “routine business on behalf of the secretary.”

Mr. Biden has said that would not accept a resignation from Mr. Austin if he were to offer one, despite the blistering criticism from GOP lawmakers regarding the lack of transparency from the Pentagon. The White House press secretary, Karine Jean-Pierre, said that Mr. Biden maintains “complete confidence” in Mr. Austin.

In light of the communication breakdown around Mr. Austin’s cancer treatment, the White House chief of staff, Jeff Zients, asked the departments of Cabinet heads to review their protocols for delegating authority and ensure they are in line with existing standards.

In a memo, Mr. Zients told department heads to notify the White House in the “event of a delegation of authority or potential delegation,” adding that “when a Cabinet Member is traveling to areas with limited or no access to communication, undergoing hospitalization or a medical procedure requiring general anesthesia, or otherwise in a circumstance when he or she may be unreachable.”

Republicans have criticized the communication breakdown, with Senator McConnell calling the incident a “dereliction of duty.” President Trump and his allies in the GOP have called on Mr. Austin to resign. “Failed Secretary of Defense Lloyd Austin should be fired immediately for improper professional conduct and dereliction of duty,” Mr. Trump said.