US President Donald Trump said Wednesday he has "total confidence" in Secretary of State Rex Tillerson following an explosive report that the top diplomat had referred to Trump as a "moron."

"It was fake news. It was a totally phony story," Trump told reporters, referring to an NBC News report that quoted senior administration officials as saying Tillerson had called Trump a "moron" last summer during a meeting at the Pentagon.

"Total confidence in Rex. I have total confidence," said Trump, hours after Tillerson denied that he had considered quitting this summer.