US defence secretary Lloyd Austin has been admitted to hospital for symptoms suggesting he has an "emergent bladder issue", the Pentagon has confirmed.
Mr Austin is just below the president in the military chain of command and must be on call to immediately respond to any crisis.
The Pentagon said he has transferred the duties of his office to deputy secretary Kathleen Hicks.
Mr Austin, 70, was transported to Walter Reed National Military Medical Center, in Maryland, at around 2.20pm on Sunday.
He was diagnosed for prostate cancer in early December, and had surgery on 22 December, but did not tell the President Joe Biden and other senior figures until days after complications forced him into intensive care on 1 January.
He admitted he "did not handle [the situation] right" and said he should have told the president.
His slow disclosure of his condition prompted an internal Pentagon review and an inspector general review into his department's notification processes.
Mr Austin was taken back to hospital by ambulance with severe pain 10 days after his surgery.
President Biden previously said it was poor judgement from Mr Austin not to tell him he was in intensive care.
However, he said he still had confidence in him.
Republicans, including former President Donald Trump, called for Austin to be removed from his job.
Mr Austin was scheduled to depart for Brussels on 13 February to hold a meeting of the Ukraine contact group, which he established in 2022 to coordinate military support for Kyiv after Russia's invasion.
After that engagement, he was scheduled to attend a regular meeting of NATO defence ministers.