Defense Secretary Lloyd Austin was taken back to the hospital on Sunday afternoon by his security detail for symptoms related to a possible bladder issue, and later transferred his responsibilities to his top deputy, the Pentagon announced.
Austin is battling prostate cancer and has been recovering from surgery over the past few months.
The Pentagon said that Austin initially had retained all the responsibilities of his post when he entered the hospital.
On his way to Walter Reed National Military Medical Center, Austin brought along all "unclassified and classified communication systems necessary to perform his duties," according to Pentagon press secretary Maj. Gen. Pat Ryder.
But the Pentagon hours later issued an update, saying that Austin had transferred his duties to Deputy Defense Secretary Kathleen Hicks just before 5 p.m. ET.
"The Chairman of the Joint Chiefs of Staff, the White House, and Congress have been notified," the Pentagon said. "We will provide additional updates on Secretary Austin's condition as soon as possible."
Later Sunday night, Walter Reed doctors said that Austin was admitted to the critical care unit.
"At this time, it is not clear how long Secretary Austin will remain hospitalized," the doctors said. "His cancer prognosis remains excellent."
The Pentagon's disclosure of Austin's hospitalization and its update avoided a repeat of a recent situation where Austin and his staff failed to inform top government officials that Austin was in the intensive care unit for complications related to his cancer surgery.
In January, Austin came under fire after the Pentagon waited days to inform the White House and the public that he was in the ICU for unknown reasons at the time.
Doctors at Walter Reed later disclosed the prostate cancer diagnosis and released details of his hospital visits.
Still, several lawmakers called on Austin to resign for the lack of transparency, though the White House rebuked those demands and doubled down on its support for the Defense Secretary as he battles cancer.
Austin's re-hospitalization on Sunday comes just over a week after he publicly apologized for hiding that earlier hospital visit and pledged to be more transparent.
"We did not handle this right. And I did not handle this right. I should have told the president about my cancer diagnosis. I should have also told my team and the American public, and I take full responsibility," Austin said at a Pentagon briefing.