If US President Donald Trump ordered a nuclear strike that was not legal, the top US nuclear commander says he would not carry it out.
US Air Force General John Hyten, who is ultimately responsible for launching a nuclear strike, said in this scenario he would instead present the president with alternative options.
General Hyten told the Halifax International Security Council: "If you execute an unlawful order, you will go to jail - you could go to jail for the rest of your life.
"It applies to nuclear weapons, it applies to small arms... it applies to everything and we apply it as we go through it."
"The way the process works, is it's simple: I provide advice to the president, he'll tell me what to do, and if it's illegal, guess what's going to happen? I'm going to say, 'Mr President, that's illegal.' And guess what he's going to do? He's going to say, 'What would be legal?'
"And we'll come up with options with a mix of capabilities to respond to whatever the situation is, and that's the way it works. It's not that complicated."
General Hyten added that he had discussed the scenario with Mr Trump and that he thought about the scenario often.
"We think about these things a lot. When you have this responsibility, how do you not think about it?"
According to the US laws of armed conflict, a president must consider necessity, distinction, proportionality and unnecessary suffering before launching any attack.
The comments come amid heightened tensions between the US and North Korea, with inflammatory comments issued from both sides.
Kim Jong Un has repeatedly ignored warnings to cease nuclear tests, prompting Mr Trump to claim the US could "totally destroy" North Korea.
On his recent tour of Asia, Mr Trump, in response to being called an "old lunatic" by Pyongyang, tweeted: "Why would Kim Jong Un insult me by calling me 'old', when I would NEVER call him 'short and fat'? Oh well, I try so hard to be his friend - and maybe someday that will happen!"
President Trump has not publicly commented on General Hyten's remarks.
