An adviser to President Donald Trump said it was "simply nonsensical" to think that Secretary of State Rex Tillerson should discuss US military decisions in relation on North Korea.
Sebastian Gorka, deputy assistant to the president, made the comments to the BBC amid reports of division within the Trump administration on how to handle North Korea.
Mr Tillerson has appeared to leave open the possibility of dialogue with the rogue regime over its nuclear weapons programme.
But Mr Gorka, a hardliner in the administration, told the BBC: "You should listen to the president. The idea that Secretary Tillerson is going to discuss military matters is simply nonsensical.
"It is the job of Secretary (James) Mattis as Secretary of Defence to talk about military options, and he has done so unequivocally.
"Secretary Tillerson is the chief diplomat of the United States, and it is his portfolio to handle those issues."
Mr Gorka said Washington would use "any appropriate measures" to protect the US from threats from North Korea.
He said: "Donald Trump has been unequivocal. He will use any appropriate measures to protect the United States and her citizens. We do not telegraph our future scenarios and how we are going to react."
In Washington a Sate Department spokeswoman, Heather Nauert, appeared to hit back at Mr Gorka's comments.
She said: "He (Mr Tillerson) is a Cabinet secretary. He’s the fourth in line to the presidency. He carries a big stick.
"I think that everyone has clearly heard what Secretary Tillerson’s forceful comments have been and continue to be."
Mr Trump himself said there were "no mixed messages" from his administration.