Joe Biden’s top military adviser, Lloyd Austin, has been hospitalized because of an “emergent bladder issue”, the Pentagon said in a statement.

The defense secretary’s admission to Walter Reed national military medical center was announced early Sunday evening.

Related: Defense secretary Lloyd Austin leaves hospital after prostate cancer surgery

The deputy defense secretary Kathleen Hicks, joint chiefs of staff, White House and Congress had been notified about Lloyd’s hospitalization, the statement said. And Hicks “is prepared to assume the functions and duties of the secretary of defense, if required”, the statement added.

“At this time, the secretary is retaining the duties and functions of his office,” the statement said, adding that Austin had “traveled to the hospital with the classified and unclassified communications systems necessary to perform his duties”.

Sunday’s notification about Austin stands in stark contrast to a previous hospitalization that the defense secretary underwent late last year after he was admitted for complications following prostate cancer surgery. The White House appeared to be unaware of Austin’s earlier hospitalization for three days.

In that instance, Austin underwent surgery at Reed hospital on 22 December 2023. He was discharged the following day but returned on 1 January. It wasn’t until 4 January that Hicks, Biden’s national security adviser Jake Sullivan and then the president were notified of Austin’s diagnosis, treatments or hospitalization.

The Pentagon then did not publicly release any notification about Austin’s hospitalization and absence from work until 5 January.

That prompted a political backlash, including an investigation by the defense department inspector general. The Pentagon later said the Austin’s chief of staff was sick with the flu, exacerbating the delay in information about the secretary’s medical condition.

The national security council spokesperson, John Kirby, said Austin’s participation in national security affairs “was no different than it would be on any other given day, except that he was briefing the president on options and engaged in the discussions from the hospital”.

But the appearance that the links in a crucial chain of command during a moment of rising global tensions and US military action against Iran-backed militias in Iraq, Syria and Yemen caused significant concern about communications within the administration.

Austin reportedly orchestrated and then watched in real time from his hospital room as US retaliatory strikes against Houthi militias were launched ahead of his 15 January discharge.

That came after the Senate armed services committee chair, Jack Reed, a Democrat, and his counterpart, the Republican senator Roger Wicker, sent a letter to Austin asking for an accounting of his absences from defense department headquarters.

Related: Biden warns Netanyahu against Rafah operation without ‘credible’ safety plan

“We are concerned that critical notification procedures were not followed while you were receiving medical care the past several weeks,” they wrote, adding that their committee “has serious questions about this incident, and members need a full accounting to ensure it never happens again”.

Sunday’s statement on Austin did not elaborate to what extent his more recent hospitalization had to do with the previous one.

It was announced hours after Biden said he warned Israel’s prime minister, Benjamin Netanyahu, to not launch an offensive in Rafah without a “credible” safety plan for more than 1 million Palestinians sheltering there.

The Israeli prime minister’s threatened offensive in Rafah comes as the military of Israel – a key US ally – has been aiming strikes at Gaza in response to the 7 October attack by Hamas.