Rex Tillerson
Rex TillersonReuters

Former US Secretary of State Rex Tillerson on Monday vehemently denied claims by former UN ambassador Nikki Haley that he worked to undermine President Donald Trump's agenda as part of a larger effort to "save the country".

In a new book, which will be released on Tuesday and of which excerpts were published on Sunday, Haley claims Tillerson and then-White House Chief of Staff John Kelly told her to resist some of Trump's instructions.

“Kelly and Tillerson confided in me that when they resisted the president, they weren’t being insubordinate, they were trying to save the country,” Haley wrote.

“It was their decisions, not the president’s, that were in the best interests of America, they said. The president didn’t know what he was doing,” she continued.

Haley also wrote that Tillerson warned that people would die if advisers like them did not take steps to keep Trump in check. Acknowledging that she and Tillerson had their "differences," Haley wrote that he "gave off the unmistakable impression that he knew more than everyone else in the room — including the president."

In a statement to The Washington Post, which published the excerpts of Haley’s book, Tillerson said, “During my service to our country as the Secretary of State, at no time did I, nor to my direct knowledge did anyone else serving along with me, take any actions to undermine the President.”

“My conversations with the President in the privacy of the Oval Office were always candid, frank, and my recommendations straightforward. Once the President made a decision, we at the State Department undertook our best efforts to implement that decision," added the former Secretary of State.

Tillerson, who served as Secretary of State during Trump's first year in the White House, added that Haley was "rarely a participant" in the many meetings he had with the president and that she wouldn't be in a position to know what he said.

Kelly dismissed Haley's claims about working around Trump, telling The Washington Post that if providing Trump "with the best and most open, legal and ethical staffing advice from across the [government] so he could make an informed decision is ‘working against Trump,’ then guilty as charged.”

Tillerson was dismissed by Trump in March of 2018, with the president later saying the reason for the move was Tillerson’s support for the 2015 nuclear deal with Iran, which Trump opposed and withdrew from.

Kelly left the White House last December following a 17-month stint as Chief of Staff amid reports of ongoing tensions between he and the President.