WASHINGTON — 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.

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.”