The State Department later denied he had even used the word, an issue Tillerson earlier declined to specifically address.
"The Secretary .... does not use that language to speak about anyone. He did not say that," State Department spokeswoman Heather Nauert said at a briefing.
The top U.S. diplomat, whose tenure has been dogged with rumours about unhappiness with Trump's policies and rhetoric, said he was as committed to Trump's agenda today as he was when he accepted the offer to serve as secretary of state.
The episode is the latest controversy to embroil Trump's administration which has witnessed a string of high-profile departures and firings in recent months, including his chief of staff, national security advisor and the former FBI director.
NBC reported that in a session with Trump's national security team and Cabinet officials at the Pentagon, Tillerson had openly criticized the president and referred to him as a "moron," citing three officials familiar with the incident.
Tillerson sidestepped the issue when taking questions after making a statement at a hastily organised news conference.
"I'm not going to deal with petty stuff like that," he said, adding, "I'm not from this place (Washington), but the places I come from we don't deal with that kind of petty nonsense."
Tillerson spoke after NBC reported that Vice President Mike Pence and other top officials had intervened to persuade him not to resign this summer as tensions rose between him and Trump.
"The vice president has never had to persuade me to remain as secretary of state because I have never considered leaving this post," Tillerson said.
"My commitment to the success of our president and our country is as strong as it was the day I accepted his offer to serve as secretary of state," Tillerson said.
Nauert said Tillerson and Trump had spoken later on Wednesday and that it was a "good conversation". Tillerson did not offer an apology to Trump because "one was not needed".
Tillerson, the former CEO of Exxon and former president of the Boy Scouts, said of Trump: "He's smart. He demands results."
Trump later told reporters in Las Vegas: "I'm very honoured by his comments. It was fake news, it was a totally phony story. ... It was made up by NBC. They just made it up. ... Total confidence in Rex. I have total confidence."
Trump had appeared to undercut Tillerson over the weekend when the president tweeted that he told him that he was "wasting his time" trying to negotiate with North Korean leader Kim Jong Un over Pyongyang's nuclear and missile programs.
Tillerson offered a vigorous defence of both the U.S. president and his foreign policy even though the White House and State Department have at times appeared to differ on policy.
"President Trump's foreign policy goals break the mold of what people traditionally think is achievable on behalf of our country," Tillerson said.
FOREIGN POLICY CONFUSION
The embarrassing episode underscored the sense of disarray that U.S. friends and foes alike have detected in their dealings with Trump's foreign policy apparatus and could further undermine U.S. credibility in world affairs.
In a tweet, Trump earlier urged NBC to apologise for its story, but NBC News anchor Hallie Jackson said on air: "NBC will not be issuing an apology to America as the president is calling for because again ... the secretary did not refute directly some of the key points" in the story.
Several NBC journalists who reported the story also stood by their piece, saying on MSNBC that their reporting was true.
Defense Secretary Jim Mattis has played down any tensions between Trump and Tillerson over their apparent split, most recently over North Korea.
Some administration officials have privately described Tillerson as chafing against some of the president's pronouncements and off-the-cuff decisions, sometimes contrary to advice from senior advisers.
One U.S. official said the view of many within the administration was that despite Tillerson's denial of having contemplated resignation, "it's only a matter of time" before he does consider it.
The official, speaking on condition of anonymity, said there was no reason to believe that Trump would give up his habit of publicly contradicting Tillerson and that each time speculation on his future would resurface.
Tillerson has often found himself at odds with the president on a range of issues, according to current and former U.S. officials and media reports.
He has taken a more hawkish view on Russia and tried to mediate a dispute among key U.S. Mideast allies after four Arab nations boycotted Qatar over its alleged extremist ties.
Tillerson also appeared to distance himself from Trump's response to violence in Charlottesville, Virginia this summer, saying at the time "the president speaks for himself" when asked about Trump's values.
Senator Bob Corker, a Tennessee Republican, said Tillerson was working under difficult circumstances because some in the administration are undermining his authority by trying to act as secretary of state on a daily basis. He declined to name names.
Corker, who is chairman of the Senate Foreign Relations committee, was asked whether he supported Tillerson, and said:
"As a team, Tillerson, Mattis and (White House Chief of Staff John) Kelly help separate us from chaos, so I absolutely support 'em. Absolutely."
Tillerson was confirmed by only 56-43 at his Senate confirmation hearing in January, an unusually low confirmation for a secretary of state.
Many members of Congress, including Republicans, strongly object to his plans to slash the State Department and foreign aid budgets.
(Reporting By Doina Chiacu and Yara Bayoumy; Additional reporting by Susan Heavey, Matt Spetalnick, Mohammad Zargham, Patricia Zengerle, Tim Ahmann, Steve Holland, Jeff Mason, Jonathan Landay, David Alexander and Susan Cornwell in Washington; Writing by Yara Bayoumy; Editing by Jeffrey Benkoe and James Dalgleish)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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