Nikki Haley, former US ambassador to the UN, has said two top White House aides encouraged her to undermine President Donald Trump.
In a new book, Ms Haley says then-Chief of Staff John Kelly and then-Secretary of State Rex Tillerson told her to resist some of Mr Trump's demands.
They reportedly told her they were "trying to save the country".
There was no immediate comment from Mr Tillerson. Mr Kelly said he had wanted the president to be fully informed.
"If by 'resistance' and 'stalling' she means putting a staff process in place... to ensure [Mr Trump] knew all the pros and cons of what policy decision he might be contemplating so he could make an informed decision, then guilty as charged," Mr Kelly told US broadcaster CBS.
Mr Trump tweeted his approval of the book, writing: "Good luck Nikki!"
What does she say in the book?
Ms Haley says Mr Kelly and Mr Tillerson told her they "weren't being subordinate, they were trying to save the country".
"It was their decisions, not the president's, that were in the best interests of America, they said," she wrote in her book With All Due Respect, which was seen by the Washington Post before its release on Tuesday.
Mr Tillerson, she added, told her people would die if the president were not restrained.
Ms Haley, 47, said she had refused the request from Mr Kelly and Mr Tillerson, and called it "dangerous" and "offensive".
"Instead of saying that to me they should have been saying that to the president, not asking me to join them on their sidebar plan," she told CBS.
"It should have been - go tell the president what your differences are and quit if you don't like what he's doing. But to undermine a president... it is really a very dangerous thing and it goes against the constitution, and it goes against what the American people want. It was offensive."
The former ambassador said she disagreed with the president over his handling of Russian President Vladimir Putin at a summit in Helsinki in 2017.
She also wrote that his comments after the deadly white supremacist rally in Charlottesville in 2017, that there were good people on "both sides", had been "hurtful and dangerous". A counter-protester, Heather Heyer, was killed at the demonstration.
But Ms Haley also said she supported a number of Mr Trump's policies that others within the administration opposed - such as his decisions to pull the US out of a nuclear deal with Iran, and to withdraw from the Paris climate agreement.
In the interview with CBS, she also criticised House Democrats' moves to impeach the president, saying that impeachment is "like the death penalty for public officials".