The Pentagon has been criticized for keeping U.S. Defense Secretary Lloyd Austin's hospitalization secret for five days, after he experienced complications following an elective surgery.

Austin, who is 70, sits just below President Joe Biden at the top of the chain of command of the U.S. military and his duties require him being available at a moment's notice to respond to any manner of national security crisis.

It is not clear whether Austin ever lost consciousness before or after he was admitted to Walter Reed National Military Medical Center on New Year's Day.

The Pentagon Press Association, in a letter to Pentagon officials, criticized the Defense Department's secrecy, saying that Austin was a public figure who had no claim to medical privacy in such a situation.

'At a time when there are growing threats to U.S. military service members in the Middle East and the U.S. is playing key national security roles in the wars in Israel and Ukraine, it is particularly critical for the American public to be informed about the health status and decision-making ability of its top defense leader,' it wrote.

The Pentagon Press Association letter noted that even U.S. presidents disclose when they must delegate duties due to medical procedures.

The Pentagon did not say what the elective surgery or complications were, not the extent to which his duties were assumed by his deputy, Kathleen Hicks.

Those duties include being ready and available to respond to an incoming nuclear attack.

'He is recovering well and is expecting to resume his full duties today,' Air Force Major General Patrick Ryder, the top Pentagon spokesperson, said in a statement on Friday.

Just a day earlier, Ryder held a televised news briefing that conveyed the sense of business as usual at the Pentagon, offering Austin's condolences to ally Japan following its New Year's Day earthquake, for example.

But the past week has been anything but normal for the Pentagon, with U.S. troops in the Middle East wrestling with the regional fallout from the unfolding Israel-Hamas war and carrying out a U.S. retaliatory strike in Baghdad on Thursday.

The way the Defense Department handled Austin's hospitalization stands in contrast to how the State Department dealt with then-Secretary of State Colin Powell's prostate surgery on Dec. 15, 2003.

The State Department spokesman at that time issued a statement in the morning making public that Powell, a retired four-star general and former chairman of the Joint Chiefs of Staff, was in surgery at Walter Reed Army Medical Center and would remain there for several days before returning home.