According to one official, the Biden administration was not informed for several days that US Defense Secretary Lloyd Austin had been hospitalized.
Mr Austin, 70, was admitted to Walter Reed Medical Center on Monday due to post-surgery complications.
According to a BBC official, the White House was not informed of this until at least Thursday morning.
Mr Austin has admitted fault for the lack of communication.
“I recognize that I could have done a better job of informing the public,” he said in a statement.
“I commit to doing better.”
In the US military’s chain of command, the defense secretary is just below the president.
Mr. Austin said that it was “important to say: this was my medical procedure, and I take full responsibility for my decisions about disclosure”.
“I am very glad to be on the mend and look forward to returning to the Pentagon soon.”
He is still believed to be in the hospital, but a defense department spokesperson quoted by the AFP news agency said he returned to full duty on Friday.
It is unclear how many of Mr Austin’s responsibilities he was able to carry out due to his illness, or how much assistance Deputy Secretary of Defense Kathleen Hicks provided.
Officials told CNN that she had taken over his duties while he was in the hospital while she was on vacation in Puerto Rico.
Meanwhile, Joe Biden reportedly had a “warm” conversation with Mr Austin on Saturday.
“The president has complete faith in Secretary Austin.” “He’s excited to be back at the Pentagon,” one official told AFP.
Republicans have been vocal in their concern about the situation.
“The secretary of defense is the key link in the chain of command between the president and the uniformed military, including the nuclear chain of command, when the weightiest of decisions must be made in minutes,” the senator said in a statement.
“If this report is true, there must be consequences for this shocking breakdown.”
While Senator Roger Wicker welcomed Mr Austin’s recovery, he noted that “the fact remains that the Department of Defense deliberately withheld the secretary of defense’s medical condition for days.” That’s not acceptable.”
In a letter to the Pentagon on Friday, the Pentagon Press Association, comprised of journalists who cover the defense department, also criticized the apparent lack of transparency.
“At a time when there are growing threats to US military service members in the Middle East and the US is playing key national security roles in the wars in Israel and Ukraine, the American public must be informed about the health status and decision-making ability of its top defense leader,” the report said.
In 2020, Mr. Austin, a retired four-star general, will become the first Black American defense secretary.