No, but they sure would be “outraged”. This would be “not acceptable”, and they would strongly “condemn” them. That would put them in their place.
The Korean War was never ended, there is an armistace. It was a UN action, thank you President Truman for subverting us to this second class status. So, would not the UN now have to approve a restart of a shooting war? Unless NK actually did something directly against the US, alone, where is our authority to in effect declare war upon them regardless of what they did. Why, we never even blew them off the planet after the Pueblo incident of the 60s wherein we had the right to wipe them out IMO.