Possible U.N. Sanctions an act of war?

In light of the U.S. consideration to push the U.N. security council to take action against NK for refusing to return to international talks, NK responded by saying any U.N. penalties would be considered an "act of war". Although I feel these threats are foundationless...and just KJI's way of keeping up with his persona, what could increased economic sanctions against the nation do to its population? Although S. Korea pushed for the chance to engage the North in more talks, as it will always do, and I cant blame them, the question still stands as to what, if any actions the security council could take and the impact they will have on the Norths struggling infrastructure.