Any North Korean attack on an American ally will meet with an “overwhelming” counterattack from the United States, particularly if the regime uses nuclear weapons.

“Due to some of the provocations out of North Korea and other challenges that we jointly face, I want to make certain that Article Five of our mutual defense treaty is understood to be as real to us today as it was a year ago, five years ago and as it will be a year and 10 years from now,” Defense Secretary Jim Mattis told reporters before a meeting with Japanese Prime Minister Shinzo Abe on Friday.