Defense Secretary Lloyd Austin has been called to testify before congressional lawmakers to explain his secretive hospitalization earlier this month.

Austin and the Pentagon have come under heavy scrutiny for not being more transparent about the secretary's hospitalization and communication gaps that left senior officials and the White House unaware of his condition or whereabouts for several days.

In a letter dated Thursday, House Armed Services Committee Chairman Mike Rogers, R-Alabama, said he spoke with Austin after news broke that he had been hospitalized for complications from an elective surgery.

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U.S. Secretary of Defense Lloyd Austin looks on during a joint press conference with Israeli Defense Minister Yoav Gallant at Israel's Ministry of Defense in Tel Aviv, Israel, on Dec. 18, 2023. Austin has come under fire for his secret hospitalization earlier this month. (Reuters/Violeta Santos Moura)

"While you did respond to some of my questions I had for you, a concerning number of questions were not addressed," Rogers wrote. "Specifically, I am alarmed you refused to answer whether you instructed your staff to not inform the President of the United States or anyone else of your hospitalization."

"Unfortunately, this leads me to believe that information is being withheld from Congress," he added.

Austin's office said the Department of Defense provided the House Armed Services Committee three letters in a "good-faith effort" to respond to the panel while "recognizing that there is an internal 30-day review underway, and the DOD Inspector General is conducting his own review."

"The Department looks forward to continuing to work with the Committee to accommodate its legislative needs," the agency said in a statement to Fox News Digital. "As always, we will respond to congressional requests as appropriate, to include requests for the Secretary to testify. We have nothing further to provide at this time."

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Rep. Mike Rogers, R-Ala., speaks during a meeting of the House Committee on Rules at the US Capitol in Washington, DC, on July 12, 2022. The committee met to discuss the National Defense Authorization Act for 2023, Women's Health Protection Act, Ensuring Access to Abortion Act, Ensuring Access to Abortion Act, and the Active Shooter Alert Act. (Photo by Oliver Contreras / AFP)

The call to testify came after reports that Austin's aide asked first responders to remain "subtle" and not use sirens or lights during while transporting him from his home on New Year's Day to the Walter Reed National Military Medical Center, according to a 911 call.

Austin returned to work in a virtual capacity on Jan. 5 while still hospitalized, even authorizing airstrikes on Yemen's Iran-backed Houthis. He was released Monday. Despite being admitted to Walter Reed upon Jan.1, the Pentagon didn't inform the public, press or Congress until Jan. 5.

Officials also acknowledged that the White House had not been informed about Austin's hospitalization until Jan. 4.

In addition to being summoned to Capitol Hill, the Pentagon is conducting an internal review into the communication lapse.

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"This is a time of immense global instability. Our country deserves reliable leadership at the department," Rogers wrote. "Maintaining the most ready and lethal force possible requires that everyone in the national security community be able to rely upon the secretary of defense’s availability and transparency."

"Regrettably, you have not exhibited these attributes throughout this most recent string of events," he added.

Defense Secretary Lloyd Austin called to testify before Congress about secretive hospitalization

House Armed Services Committee Chairman Mike Rogers, R-Alabama, said he spoke privately with Austin, who failed to provide 'candid and complete answers;