The Pentagon’s second in command, Defense Deputy Secretary Kathleen Hicks, was unaware that Defense Secretary Lloyd Austin was in the hospital when she assumed some of his duties early last week, according to a senior military official.

Pentagon press secretary Maj. Gen. Pat Ryder revealed in a statement on Friday that Austin was admitted to Walter Reed National Military Medical Center last Monday, following complications with an elective medical procedure.

A senior defense official told Fox News that Austin originally intended to work from home during the first week of January.

The press was not told of the news for days because of "medical and personal privacy issues," Ryder noted.

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Secretary Lloyd Austin

Secretary of Defense Lloyd Austin participates in a meeting with Italian Defense Minister Guido Crosetto at the Pentagon on June 23, 2023 in Arlington, Virginia. (Kevin Dietsch/Getty Images)

Also kept out of the loop for days were President Biden, National Security Advisor Jake Sullivan, the White House Chief of Staff, other senior White House officials and the second in command at the Pentagon.

Hicks, who was on a previously scheduled vacation in Puerto Rico was not told Austin had been hospitalized until Thursday. As soon as she found out her senior was hospitalized, she planned to put out a press statement and go back to Washington, D.C. on Friday, a senior U.S. defense officials confirmed with Fox News. Despite her plans, Hicks was told Austin would resume his duties on Friday.

Although Hicks was told of Austin’s hospitalization on Thursday, Ryder said, "certain operational duties" were transferred to her on Jan. 2.

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DOD second in command

U.S. Deputy Defense Secretary Kathleen Hicks speaks during a September 11th Pentagon Staff Memorial Observance ceremony at the Pentagon courtyard on September 8, 2023 in Arlington, Virginia.  (Alex Wong/Getty Images)

"On the afternoon of January 2, the Secretary of Defense transferred to the Deputy Secretary of Defense certain operational responsibilities that require constant secure communications capabilities," Ryder said. "This transfer occurs from time-to-time and is not tied chiefly to health-related matters. The deputy secretary keeps a complete suite of communications and capable staff with her at all times, regardless of geographic location."

A senior defense official added that Hicks immediately told staff to draft the public statement and congressional outreach.

"Deputy Secretary Hicks made some routine operational and management decisions for the Department over this period and was fully authorized and ready to support the President on other military matters, should the need have risen," the senior defense official said.

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The Pentagon

The Pentagon is seen from a flight taking off from Ronald Reagan Washington National Airport in Arlington, Virginia.  (Alex Wong/Getty Images)

The news came as tensions remained heightened in the Middle East when a U.S. strike killed four members of an Iran-aligned militia group in Baghdad and two suicide bombs in Iran left at least 103 people dead. Israel also continued its bombardment of Gaza while Austin was hospitalized.

Austin remains hospitalized at Walter Reed, according to Ryder. He added that a date for his release is not yet available.

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It is still unclear why Austin was hospitalized in the first place, or what the elective procedure was or when it occurred.

Fox News’ Sarah Rumpf-Whitten and Michael Dorgan contributed to this report.