(CNN) — Republicans, including former Vice President Mike Pence, blasted Secretary of Defense Lloyd Austin over the weekend for waiting days to notify President Joe Biden that he was hospitalized.

Austin was admitted to the hospital on New Year’s Day due to complications from an elective surgery, but Biden was not informed that his civilian leader of the military was hospitalized until January 4, when national security adviser Jake Sullivan informed him that evening, a source familiar with the matter told CNN.

Responding to Austin’s hospital stay, Pence wished Austin well but slammed his lack of transparency as “totally unacceptable.”

“I believe the American people have the right to know about his medical condition, about the reasons for it,” he told CNN’s Jake Tapper on “State of the Union,” characterizing Austin’s actions as a “dereliction of duty.”

Sen. Roger Wicker, the highest-ranking Republican on the Senate Armed Services Committee, called the withholding of information Austin’s hospitalization “unacceptable,” in a statement released Saturday.

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

Wicker said the lack of transparency on Austin’s hospitalization “erodes trust in the Biden Administration.”

He added, “Worryingly, we now have more questions than answers. Why was the notification process under 5 U.S.C. 3349 not followed and who made the determination not to follow it?” 5 U.S.C. 3349 is the US code for reporting vacancies in an office, which applies to the head of each executive agency.

Republican Sen. James Lankford of Oklahoma on “Fox News Sunday” called the lack of disclosure over Austin’s hospitalization “shocking.”

“It’s pretty shocking on this because when you’re the secretary of defense, you need to make everyone aware that you’re actually going out of pocket,” Lankford said.

Lankford went on to say the issue was not just that Austin was absent from his position, but that key branches of government weren’t aware.

“Apparently, the National Security Council didn’t know it, the White House didn’t know it, Congress didn’t know it. We’re at a time with a lot of turmoil internationally,” Lankford said.

Rep. Jim Clyburn, assistant Democratic leader in the House, told Tapper he disagreed with Pence that Austin’s actions were a “dereliction of duty,” calling Austin a “stand-up guy” and a “great defense secretary.”

“Now we have some laws in this country, HIPAA laws, that keep us out of people’s medical businesses, and I do believe this man has as much right to be protected by those laws, and be subjected to those laws, as everybody else. He does have a duty to keep the public informed. And I don’t know whether it was him, or someone inside the military establishment that decided to do it this way, but I am sure he will do a little better going forward as he said he would.”

Secretary of State Antony Blinken, in response to a reporter’s question at a news conference in Qatar on Sunday, said he “wasn’t aware” of Austin’s medical issue at the time.

“I talked to Lloyd last weekend before this incident and I know that he’s put out a statement addressing it,” Blinken said.

He added that “it remains one of the great privileges of my career – over 30 years now serving in government – to serve alongside Lloyd Austin. He is an extraordinary leader for this country, in uniform and out of uniform, and it has been a highlight of my service to serve alongside him and I’m very much looking forward to seeing him fully recovered and working side by side in the year ahead.”

Austin is a critical member of Biden’s cabinet and holds one of the most important roles in the national security establishment — particularly as the US military faces increased tensions in the Middle East.

The same day he was hospitalized, Austin was among Biden’s top national security officials who participated in a New Year’s Day call with the president to discuss, among other things, the escalating situation in the Red Sea, a source familiar with the call told CNN.

It was not clear whether the call — which was said to have taken place in the morning — was before or after Austin was hospitalized. But the secretary sounded fine during the meeting, the source said at the time.

During Austin’s hospitalization, the US carried out a strike in Baghdad against the commander of a pro-Iran militia. Austin gave authorization for the strike before he was hospitalized, said Pentagon press secretary Maj. Gen. Pat Ryder.

Deputy Defense Secretary Kathleen Hicks periodically assumed the duties of the defense secretary while she was on vacation in Puerto Rico during the time Austin was hospitalized, two US officials said. Hicks had arrived in Puerto Rico prior to Austin’s hospitalization.

Austin has since reassumed his full duties. He spoke to Biden on Saturday evening, according to a White House official, who said the “president has complete confidence in Secretary Austin and is looking forward to him being back in the Pentagon.”

On Saturday evening, Austin thanked the “amazing” staff at Walter Reed National Military Medical Center for the care he has received and said he is “on the mend” and looking forward to returning to the Pentagon.

He acknowledged “media concerns about transparency” and said “I commit to doing better” in the statement, which totaled seven sentences. But he did not apologize for failing to notify the public or the press in a timely fashion. Senior administration and military officials who are hospitalized normally put out a statement within 24 hours.

This story has been updated with additional information.

CNN’s MJ Lee, Oren Liebermann, Haley Britzky, Natasha Bertrand and Kevin Liptak contributed to this report.