In a follow-up tweet, Donald Trump doubled down, claiming that the "White House is running very smoothly despite phony Witch Hunts". "He always knows where I stand and he and I both know this story is total BS", Kelly said in a statement.
Kelly, in a statement, says he and Trump have "an incredibly candid and strong relationship".
Previous reports have suggested that Kelly's power in the White House has waned and that Trump had considered firing him.
Officials told NBC that Kelly questioned aloud why Porter's alleged victims "wouldn't just move on".
Yes, this does sound bad. As tension remains in the White House, it was only a matter of time before the president spoke out.
"Kelly appears to be less engaged, which may be to the President's detriment", a senior official said.
General Kelly is Mr Trump's second chief of staff after Reince Priebus, who was accused of leaking information to reporters, resigned in July 2017.
Unlike President Trump, who would never be driven by anything besides cold logic.
"I don't think anybody is surprised that he and the President have had disagreements in the past", the official said.
President Donald Trump reportedly considered withdrawing USA troops from the Korean Peninsula.
Mr. Kelly said he is "committed to the president, his agenda, and our country"'.
Wait, what??? If this terrifying anecdote is true, Kelly deserves at least some credit for preventing utter political chaos over the last few months.
These officials told NBC that Kelly is in the Oval Office "more than anyone else".
The US network reported on Monday that Mr Kelly has privately criticised the president's knowledge on issues including immigration. In one heated exchange between the two men before February's Winter Olympics in South Korea, Kelly strongly - and successfully - dissuaded Trump from ordering the withdrawal of all USA troops from the Korean Peninsula, according to two officials. "We've got to save him from himself".