Washington DC - US Secretary of Defense Lloyd Austin was admitted to a critical care ward with a bladder issue after he transferred his duties to his deputy Sunday, the Pentagon said, as he battles prostate cancer.

Deputy Secretary of Defense Kathleen Hicks "assumed the functions and duties" just before 5:00 PM, Pentagon spokesperson Pat Ryder said in a statement, adding that the White House and Congress had been informed.

Austin was "admitted into the critical care unit at Walter Reed National Military Medical Center for supportive care and close monitoring," the Pentagon said in a later statement, citing his doctors.

The latest health scare came weeks after it emerged that Austin (70) had kept previous hospital stays secret and had not immediately informed US President Joe Biden of his cancer diagnosis, sparking criticism amid crises in the Middle East and Ukraine.

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Austin effectively vanished from the public eye for treatment for prostate cancer in December and again in January after suffering complications from the procedure.

This time, the public was alerted around two hours after he was sent to the hospital on Sunday afternoon.

Austin "was transported by his security detail" to the hospital, Ryder said in the earlier statement.

Ryder noted initially that the defense chief brought along classified communications systems and would be retaining "the functions and duties of his office."

However, the announcement that Hicks would instead be taking over came just a few hours later.

"At this time, it is not clear how long Secretary Austin will remain hospitalized," said the latest statement, attributed to Dr. John Maddox and Dr. Gregory Chesnut of the Walter Reed National Military Medical Center in Maryland.

"The current bladder issue is not expected to change his anticipated full recovery. His cancer prognosis remains excellent."

Austin apologized this month after coming under heavy political fire for keeping the previous hospital stays secret.

"I should have told the president about my cancer diagnosis," he told journalists on February 1.

At the time, he said he was still in recovery, suffering from leg pain, and using a golf cart for transportation inside the Pentagon.

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The undisclosed absences – as well as this current hospital stay – come at a time when the United States faces a spiraling crisis in the Middle East, with American forces in Iraq and Syria facing near-daily attacks in retaliation for Washington's steadfast support of Israel's brutal assault on Gaza.

The top US defense official is also a key figure in attempts by the Biden administration to maintain military aid for Ukraine's fight against Russia's invasion, as some members of Congress refuse to authorize new funding.

Various Republican lawmakers previously called for Austin to be sacked, but Biden, while lamenting the Pentagon chief's lapse in judgment, has said he remains confident in his defense secretary.

Austin has gained a reputation as a largely apolitical public servant who is most comfortable with US troops.

A commanding presence at well over six feet tall, he is an intensely private person who eschews the spotlight, which he said played into his decision to keep the cancer diagnosis secret.

But he acknowledged that "taking this kind of job means losing some of the privacy that most of us expect. The American people have a right to know if their leaders are facing health challenges that might affect their ability to perform their duties, even temporarily."