Updated

Secretary of Defense Lloyd Austin was transferred to the critical care unit at Walter Reed National Military Medical Center Sunday night after being transported to the hospital earlier in the day.

Austin was transported to the hospital by his security detail on Sunday for symptoms suggesting an emergent bladder issue, according to a statement released by the Department of Defense from his doctors.

Following a series of tests and evaluations, Austin was admitted into the critical care unit Sunday night for supportive care and close monitoring, the statement added.

DEFENSE SEC. AUSTIN BACK IN HOSPITAL FOR BLADDER ISSUE, TRANSFERS POWERS TO HICKS: PENTAGON OFFICIALS

Defense Secretary Lloyd Austin

Secretary of Defense Lloyd Austin was transferred to the critical care unit at Walter Reed National Military Medical Center Sunday night after being transported to the hospital earlier in the day. (Ian Waldie/Bloomberg via Getty Images)

"At this time, it is not clear how long Secretary Austin will remain hospitalized," the statement said. "The current bladder issue is not expected to change his anticipated full recovery. His cancer prognosis remains excellent. Updates on the Secretary's condition will be provided as soon as possible."

Austin's powers have been temporarily transferred to Deputy Defense Secretary Kathleen Hicks as of Sunday afternoon.

The defense secretary's planned trip to Brussels this week for meetings on Ukraine and NATO has been canceled, and the Wednesday Ukraine Defense Contact Group will meet virtually, the department said Monday.

In December, Austin was admitted to Walter Reed and underwent prostate cancer surgery. He developed an infection a week later and was readmitted to the hospital.

Hicks filled in at the time while she was on a previously scheduled leave.

WHITE HOUSE ESTABLISHES GUIDELINES FOR CABINET NOTIFICATIONS FOLLOWING AUSTIN'S HOSPITALIZATION CONTROVERSY

Lloyd Austin returns to Pentagon

Defense Secretary Lloyd Austin was admitted into the critical care unit Sunday night for supportive care and close monitoring. (AP Photo/Susan Walsh)

President Biden, other senior administration officials and the American public were not told for days about his hospitalization or his cancer. Austin was admitted to Walter Reed on Jan.1, but the Pentagon failed to inform the public, press and Congress until Jan. 5.

Officials also acknowledged that the White House had not been informed about Austin's hospitalization until Jan. 4.

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Austin said earlier this month that he apologized directly to Biden for not giving advance notice about his hospitalization for prostate cancer treatment.

"I want to be crystal clear. We did not handle this right and I did not handle this right," Austin said during a press briefing on Feb. 1, regarding his hospitalization for prostate cancer treatment. "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. I apologize to my teammates and to the American people."

Fox News' Liz Friden and Greg Wehner contributed to this report.