The Pentagon released new details Sunday about Defense Secretary Lloyd Austin's continued hospitalization, saying he had a medical procedure Dec. 22, went home a day later and was admitted to intensive care Jan. 1 when he began experiencing severe pain.

The latest information came as members of both parties in Congress expressed sharp concerns about the secrecy of Austin's hospital stay and the fact that the president and other senior leaders were kept in the dark about it for days.

The statement, released by Air Force Maj. Gen. Pat Ryder, did not, however, provide any details about the medical procedure or what actually happened on Monday to require Austin to be in intensive care at the Walter Reed Army Medical Center.

Ryan said Austin was placed in the hospital's intensive care unit "due to his medical needs, but then remained in that location in part due to hospital space considerations and privacy."

The Pentagon's failure to disclose Austin's hospitalization, including to President Joe Biden, the National Security Council and top Pentagon leaders, for days reflects a stunning lack of transparency about his illness, how serious it was and when he may be released. Such secrecy, when the United States is juggling myriad national security crises, runs counter to normal practice with the president and other senior U.S. officials and Cabinet members.

Ryder said the National Security Council and Deputy Secretary of Defense Kathleen Hicks were not notified until Thursday, Jan. 4, that Austin had been hospitalized since Jan. 1. Ryder said Austin's chief of staff, Kelly Magsamen, was ill and "unable to make notifications before then." He said she informed Hicks and the national security adviser, Jake Sullivan, on Thursday.

Once notified, Hicks began preparing statements to send to Congress and made plans to return to Washington. Hicks was in Puerto Rico on leave but had communications equipment with her to remain in contact and had already been tasked with some secretary-level duties on Tuesday.

The Pentagon did not say if Hicks was given an explanation on Tuesday for why she was assuming some of Austin's duties, but temporary transfers of authority are not unusual and are often done without detailed explanations. Hicks decided not to return after she was informed that Austin would resume full control on Friday.

Biden was told of Austin's medical stay on Thursday by Sullivan, according to three people with knowledge of the hospitalization who were not authorized to speak publicly and spoke to the AP on condition of anonymity.

In a statement issued Saturday evening, Austin took responsibility for the delays in notification.

"I recognize I could have done a better job ensuring the public was appropriately informed. I commit to doing better," he said, acknowledging the concerns about transparency. "But this is important to say: this was my medical procedure, and I take full responsibility for my decisions about disclosure."

Austin, 70, remains hospitalized and officials have been unable to say how long he will be at Walter Reed. In his statement, Austin said he is on the mend and is looking forward to returning to the Pentagon soon, but he provided no other details about his ailment.

Sen. Roger Wicker, the top-ranking Republican on the Senate Armed Services Committee, said the episode erodes trust in the Biden administration and called on the department to provide lawmakers with a "full accounting of the facts immediately."

"I am glad to hear Secretary Austin is in improved condition and I wish him a speedy recovery," Wicker said in a statement. "However, the fact remains that the Department of Defense deliberately withheld the Secretary of Defense's medical condition for days. That is unacceptable."

It's not just Republicans expressing alarm. In a joint statement, Reps. Mike Rogers, R-Ala., and Adam Smith, D-Wash., said they were "concerned with how the disclosure of the Secretary's condition was handled."

Among the questions they had were what the medical procedure was and what the resulting complications were, how and when the delegation of his responsibilities was made, and the reason for the delay in notification to the president and lawmakers. Rogers is chairman of the House Armed Services Committee and Smith is the panel's top Democrat.

"Transparency is vitally important," said the two lawmakers. "Austin "must provide these additional details on his health and the decision-making process that occurred in the past week as soon as possible."

Secretary of State Antony Blinken voiced support for Austin at a news conference in Qatar on Sunday.

"He is an extraordinary leader in this country, in uniform and now out of uniform," Blinken said. "And it's been a highlight of my service to be able to serve alongside him,." He added: "I'm very much looking forward to see him fully recovered and working side by side in the year ahead."

Ryder said Austin is able to do his full duties, has secure communications at Walter Reed, and is in contact with his senior team, getting updates and providing guidance. He said he doesn't know if Austin will do in-person briefings this coming week.

The Pentagon Press Association, which represents journalists who cover the Defense Department, sent a letter of protest on Friday evening, calling the delay in alerting the public "an outrage."

"At a time when there are growing threats to U.S. military service members in the Middle East and the U.S. is playing key national security roles in the wars in Israel and Ukraine, it is particularly critical for the American public to be informed about the health status and decision-making ability of its top defense leader," the group said in its letter.

Other senior U.S. leaders have been much more transparent about hospital stays. When Attorney General Merrick Garland went in for a routine medical procedure in 2022, his office informed the public a week in advance and outlined how long he was expected to be out and when he would return to work.