William Hague has dismissed claims he has lost his "mojo" and is ready to resign as Foreign Secretary.
Mr Hague has faced questions about his appetite for front-line politics amid criticism of his handling of the Libyan crisis.
But, in an interview with The Sunday Telegraph, he sought to end speculation about his future and David Cameron's support for him.
"If some of the people who write about mojo came with me for a week, they would drop dead on their feet," he said.
"The Prime Minister is extremely supportive (of me) and so are the vast majority of Conservative MPs. People had better get used to the idea."
Earlier this week, senior Liberal Democrat Sir Menzies Campbell openly questioned Mr Hague's commitment to the job.
"I am not sure just how enthusiastic he is about this business," Sir Menzies said.
"It is very, very hard... It is a very, very demanding job."
Challenged about his commitment the following day, Mr Hague fuelled speculation by saying only that he would remain in the job for "an extended period of time".
Referring to the "Arab Spring", Mr Hague said: "These are historic and momentous events that are taking place.
"I say to you very seriously that all of us who have taken on the job of shouldering responsibilities at this time will see those responsibilities through for an extended period of time in the face of any criticism or setbacks."
Asked whether Mr Hague's position in Government was under threat, the Prime Minister's official spokesman said Mr Cameron was not planning a Cabinet reshuffle "any time soon".
The Foreign Secretary has been criticised over the botched SAS mission to make contact with Libyan rebels, uncertainty over the Government's position on the imposition of a no-fly zone, the slow start to the evacuation of British nationals, and his mistaken suggestion that Colonel Muammar Gaddafi had fled to Venezuela.