After being admitted to the hospital last week, Secretary of Defense Lloyd Austin transferred responsibility to Deputy Secretary of Defense Kathleen Hicks on Tuesday. But Hicks, who was on vacation in Puerto Rico at the time, was not informed about his hospitalization until Thursday, a senior defense official told NBC News.

Austin transferred “certain operational responsibilities that require constant secure communications capabilities” to Hicks on the afternoon of Jan. 2, Pentagon press secretary Maj. Gen. Pat Ryder said.

“This transfer occurs from time to time and is not tied chiefly to health-related matters,” he said. “The Deputy Secretary keeps a complete suite of communications and capable staff with her at all times, regardless of geographic location.”

U.S. Secretary of Defense Lloyd Austin was hospitalized on Jan. 1. Volodymyr Tarasov / Future Publishing via Getty Images

Hicks was informed on Thursday of Austin’s hospitalization that began on Jan. 1, a senior defense official said, adding that Hicks immediately engaged staff on the drafting of a public statement and congressional outreach.

She had begun making contingency plans to return to Washington from her vacation on Friday but was told the defense secretary was preparing to resume full communications capability and the associated operational responsibilities, which informed her decision to stay on vacation, the senior defense official said. Hicks remained in place to ensure the best communications posture in the interim, that official said.

During the three days that she took over Austin’s duties, Hicks made some routine operational and management decisions for the Department of Defense and was fully authorized and ready to support President Joe Biden on other military matters if need be, the official said.

Hicks was not the only federal official who was unaware of Austin’s hospitalization. The Pentagon waited three days after Austin arrived at Walter Reed Medical Center to inform senior officials in the White House’s National Security Council about his condition, a U.S. official confirmed to NBC News.

Asked by NBC News during a Sunday press conference in Doha, Qatar, about Austin, Secretary of State Antony Blinken said he “wasn’t aware of his medical issue” either.

“In fact, I talked to Lloyd last weekend before this incident and I know that he’s put out a statement addressing it,” Blinken said, going on to praise Austin as “an extraordinary leader for this country.”

“I’m very much looking forward to seeing him fully recovered and working side by side in the year ahead,” he added. “Again, I think he put out a statement addressing this. I’ll let that statement speak for itself.”

Austin was admitted to the hospital last week, which included spending four days in the intensive care unit, two senior administration officials previously told NBC News.

He was admitted to the hospital Monday night for “complications following a recent elective medical procedure,” Pentagon press secretary Maj. Gen. Pat Ryder said in a statement Friday evening.

Austin took responsibility for failing to disclose his condition sooner in a statement Saturday.

“I am very glad to be on the mend and look forward to returning to the Pentagon soon. I also understand the media concerns about transparency and I recognize I could have done a better job ensuring the public was appropriately informed. I commit to doing better,” Austin said. “But this is important to say: this was my medical procedure, and I take full responsibility for my decisions about disclosure.”

Austin’s hospitalization came amid mounting tensions in the Middle East. During his hospitalization, the U.S. conducted a controversial airstrike that killed the leader of an Iranian-backed militia in Baghdad and bases with Americans have been the target of attacks at least six times. The Biden administration has also been weighing options to strike Iran-backed Houthi militants based in Yemen due to their continued attacks against ships in the Red Sea in retaliation for Israel’s attacks on Palestinian communities.