Joe Biden is under mounting pressure to sack his defence chief, Lloyd Austin, after he kept the US president in the dark for four days over his hospitalisation.

Mr Austin, 70, who was still in hospital on Sunday, was admitted on New Year’s Day for what the Pentagon said were “complications” following a recent elective surgery.

But the White House was not informed of his absence until January 4, while Mr Austin’s deputy, Kathleen Hicks, was herself on holiday in Puerto Rico.

Calls for defence secretary to be replaced 

The apparent lapse came as war continues to rage in Gaza and Ukraine and has heaped pressure on the White House to take action, with Republicans calling for the defence secretary to be replaced.

“If this report is true, there must be consequences for this shocking breakdown,” said Arkansas senator Tom Cotton.

Jim Banks, a member of the House Armed Services, added Mr Austin had “been a disaster since day one”.

He “should be replaced by someone who will focus on making the military ready to fight and win wars instead of advancing woke political causes of the Biden administration”, Mr Banks said.

Available at moment’s notice 

The defence secretary sits just below Mr Biden at the top of the chain of command of the US military and his duties require his being available at a moment’s notice to respond to any manner of national security crisis.

While he and his deputy were away from the Pentagon, the US military carried out an airstrike in Baghdad, killing the leader of an Iran-backed militia.

It remains unclear the extent to which his duties were delegated to Ms Hicks, or whether Mr Austin was involved in any key decisions during his absence.

Ms Hicks was herself not informed of the reason she was stepping up to fill in for her boss, CNN reported.

But the top Republican on the Senate Armed Services Committee, Senator Roger Wicker, accused the Pentagon of failing to inform Congress immediately about such matters, as required by law.

He added the episode had further eroded the public’s trust in the Biden administration, citing past failures to quickly disclose information about national security incidents, including the appearance of a Chinese spy balloon over the United States last year.

“When one of the country’s two National Command Authorities is unable to perform their duties, military families, Members of Congress, and the American public deserve to know the full extent of the circumstances,” Mr Wicker said in a statement.

‘Dereliction of duty’ 

Mike Pence, the former vice president, told CNN: “To think that at a time when we have allies at war in Eastern Europe and here in Israel, that the leader of America’s military at the Pentagon would be out of commission for a number of days, and the President of the United States didn’t know about it.

“I think it was a dereliction of duty and the Secretary and the administration, frankly, need to step forward and give the American people the facts.”

“It is unbelievable,” Jeff Lord, who worked in the Reagan White House, told The Telegraph. “I can’t imagine how nobody in the White House knew he was in hospital and not at his job. The president should have been informed.

“This is off-the-charts irresponsible. We are in a nuclear age for starters and with what is going on in Ukraine and Israel, the negligence is stunning.”

Unclear when Mr Austin discharged 

The Pentagon, which said Mr Austin resumed his full duties on Friday, was unable to say when the defence secretary would be discharged from Walter Reed Hospital.

It also declined to disclose details of Mr Austin’s medical condition, beyond saying there were complications, following a routine procedure.

Despite being in Puerto Rico, Ms Hicks had maintained full communication with the Pentagon, a spokesman for the defence department said as it tried to contain the political fallout.

It added that Mr Austin had spoken to the president on Saturday for the first time after being admitted to hospital.

US officials speaking on condition of anonymity said Mr Biden retained full confidence in his defence chief.

Mr Austin takes ‘full responsibility’ 

An embarrassed Mr Austin said he took full responsibility for what had happened.

“I also understand the media concerns about transparency, and I recognise I could have done a better job ensuring the public was appropriately informed. I commit to doing better,” he said.

“But this is important to say: this was my medical procedure, and I take full responsibility for my decisions about disclosure.”