Bethesda, Maryland - US Secretary of Defense Lloyd Austin has prostate cancer, the hospital treating him has said, placing him at the center of a scandal over not informing the public and president sooner.

The disease was recognized early and the prognosis for a cure is "excellent," Walter Reed Military Hospital in Bethesda, Maryland - outside the US capital - announced on Tuesday.

The Pentagon in Washington has been highly criticized for not telling either President Joe Biden or the public quickly about Austin's condition.

The 70-year-old has been hospitalized since the beginning of the year due to complications following an operation at the end of December.

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The prostate cancer was diagnosed at the beginning of December, the hospital announced. Shortly before Christmas, Austin underwent a minimally invasive surgical procedure and went home the next morning.

On New Year's Day, Austin was then admitted to hospital due to complications, including nausea and severe abdominal, hip, and leg pain. An initial examination revealed a urinary tract infection and he was transferred to the intensive care unit on January 2.

According to the hospital, fluid accumulation in the abdomen caused problems.

The infection has since subsided. Austin is making progress and a "full recovery" is expected, but this could be a long process, the hospital said.

The defense secretary was never unconscious or subject to a general anaesthetic, the army hospital added.

In the US, it is typical for top officials to inform the public about the state of their health. Austin came under hefty criticism for not doing so. He publicly apologized and said he "would do better."

US National Security Council communications director John Kirby said a review would be undertaken.

"And if there’s some changes that need to be made, you know, in terms of process and procedure, we’ll do that," he told reporters at the White House. "Our main focus right now is on Secretary Austin’s health and making sure that he gets all the care and support that he needs to — to fully recover. That’s the focus."

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Kirby said Austin had already resumed all his authorities. "He’s already doing all of the functions he would normally do. He’s just doing it right now from the hospital."

White House Press Secretary Karine Jean-Pierre said Biden had "complete confidence" in Austin.

"I think the number one thing right now is for him — we want to see him back at the Pentagon — get well and back at the Pentagon," she said.

"The President appreciated Austin’s statement and taking full responsibility here. And I think that’s matters, is him getting back to the Pentagon and taking full responsibility."