The top United States commander responsible for overseeing the country’s nuclear arsenal on Saturday said he would resist an order from President Donald Trump to launch a nuclear strike if he believed it was illegal, Reuters reported.

“I think some people think we are stupid,” said Air Force General John Hyten, who heads the US Strategic Command. “We are not stupid people. We think about these things a lot. When you have this responsibility, how do you not think about it?”

General Hyten’s remarks – made in response to a question at the Halifax International Security Forum in Canada’s Nova Scotia province – come in the backdrop of continued tensions between the United States and North Korea. In August, Trump warned Pyongyang that any threat to the United States will be met with “fire and fury like the world has never seen”.

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Explaining how things work, General Hyten said he is required to advise the president and he would, in turn, instruct him what to do, CBS News reported. “And if it is illegal, guess what is going to happen? I am going to say, ‘Mr President, that is illegal.’”

The commander said Trump has to base his decision on the criteria of necessity, distinction, proportionality and unnecessary suffering. If the president asks for options that will not be deemed unlawful, General Hyten said he “will come up with options, of a mix of capabilities to respond to whatever the situation is”.

The top Air Force official said those who implement an illegal order can be jailed for the rest of their lives.