The 70-year-old's failure to disclose his hospitalization left top officials in the dark about his status as Washington struggles to contain the fallout from the Israel-Hamas war, which has sparked violence against American forces in Iraq and Syria as well as attacks on international shipping.

Austin's "prostate cancer was detected early and his prognosis is excellent," two doctors from Walter Reed National Military Medical Center said in a statement released by the Pentagon.

The cancer was detected as a result of routine screening and Austin underwent a minor surgical procedure to treat it on December 22, returning home the following day, they said.

But he was readmitted to the same hospital on January 1 due to complications "including nausea with severe abdominal, hip, and leg pain. Initial evaluation revealed a urinary tract infection," necessitating further treatment.

"He continues to make progress and we anticipate a full recovery although this can be a slow process. During this stay, Secretary Austin never lost consciousness and never underwent general anesthesia," the doctors said.

While Austin was hospitalized on January 1, the Pentagon did not make any public announcement until four days later, and also waited to notify President Joe Biden and Congress.

Some of Austin's authorities were transferred to Deputy Defense Secretary Kathleen Hicks on January 2, but she was not told that he was hospitalized until two days later, Pentagon spokesman Major General Pat Ryder told journalists on Monday.

The US National Security Advisor Jake Sullivan was informed on January 4, bringing the White House into the loop, while Congress was not told until the day after that -- the same day the Pentagon made a public announcement.

Some Republican lawmakers have called for Austin to resign or be fired, but the White House has stood by the secretary, and Ryder said the secretary has no plans to resign.