New details have emerged on the rift between White House chief of staff John Kelly and President Donald Trump, with one former administration official saying Mr Kelly privately called Mr Trump "an idiot" last year.
Mr Kelly's insult, confirmed to the Associated Press by the former official, came as his clashes with Mr Trump over policy and personnel grew louder and more frequent.
The chief of staff, who has cast himself as safeguarding the public from the president, has also threatened to quit the White House on several occasions.
Mr Kelly's disparaging remark was first reported on Monday by NBC News.
In a statement, Mr Kelly called the report "total BS" and characterised his relationship with Mr Trump as "incredibly candid and strong".
He added of the president: "He always knows where I stand and he and I both know this story is total BS."
Mr Kelly's top aide Zachary Fuentes also disputed the characterisation, saying he had never heard Mr Kelly describe the president that way.
"Remember, he is a Marine. Once a Marine, always a Marine," said Mr Fuentes. "The office of the commander in chief is held to the highest regard."
Mr Trump appeared to react to the NBC report on Twitter, tweeting: "The Fake News is going crazy making up false stories and using only unnamed sources (who don't exist)."
He added: "The White House is running very smoothly."
In recent months, Mr Trump has chafed at Mr Kelly's management style, and has occasionally talked with friends about replacing him.
In his early days in the White House, Mr Kelly imposed strict controls on access and the flow of information to Mr Trump, though his direct influence has waned somewhat since then, aides said.
Kelly allies insist he has merely trained the staff to follow his management protocols, but officials note that Mr Trump has grown more willing to act unilaterally, ignoring or simply not seeking out the advice of his top aide.
The disagreements between the retired four-star general and the businessman-turned-president have grown more animated, and on one such occasion last year Mr Kelly blasted the president as "an idiot" to staffers, the former administration official told the AP.
The public revelation of an insult directed at the president's intelligence is reminiscent of leaks last year that then-secretary of state Rex Tillerson called Mr Trump a "moron".
That episode created what White House officials described as an irreparable rift between Mr Trump and his chief diplomat, and ultimately led to Mr Tillerson's unceremonious March firing.
Mr Kelly said NBC's report "is another pathetic attempt to smear people close to President Trump and distract from the administration's many successes".
Still, Mr Kelly has told people close to him that while he wanted to make the one-year mark in the position - that would mean late July - he is no longer confident he will.
Mr Fuentes, meanwhile, said that Mr Kelly is distressed to see his name tainted, but added: "The reason that Kelly's here is because he believes in this country and he's a man of service."
"His relationship with the president is great, never been better," he added. "They aren't having any issues whatsoever."