In Sunday's interview, Tillerson would not deny using the insult about the president.
Tillerson said he and Trump work closely on matters of foreign policy and he said his job is to execute the decisions the president makes.
US Secretary of State Rex Tillerson said Sunday his diplomatic efforts will continue as long as they possibly can despite the saber-rattling on both sides of the Pacific. It was after that session that Tillerson, in a private conversation with fellow U.S. officials, exasperatedly called the President a "moron", a comment that sparked new questions about the two men's relationship.
"These are the games of Washington", Tillerson said. CNN host Jake Tapper repeatedly asked him about the allegation, but Tillerson insisted he would not play "games" by answering.
The reported tension between the president and the top USA diplomat comes as the US faces a slew of foreign policy challenges. "I'm just not going to be part of this effort to divide this administration".
International Monetary Fund says Zambia public debt rising at unsustainable pace
The Fund had already cut its 2017 forecast by 0.3 percentage points in July from April and left its latest forecast unchanged. India's growth rate in 2016 was 7.1 per cent, which saw an upward revision of 0.3 percentage points from its April report.
"I am fully committed to his objectives", Tillerson continued.
But Trump's recent Twitter messages appeared to undercut Tillerson's efforts, prompting the Senate foreign relations committee chairman Bob Corker to complain that Trump was publicly castrating Tillerson and hurting diplomatic talks.
Corker has already been a target of Trump's Twitter tirades.
"US Republican senator Bob Corker stepped up his public feud with Donald Trump on Friday, saying the presidents undermining of his secretary of state was like castrating him in public".
"I'm not playing", Tillerson told Tapper, after Tapper asked about the alleged "moron" comment.