Mattis: If North Korea fires missile at US, it's 'game on'

North Korean leader Kim Jong Un guides on the spot the underwater test-fire of strategic submarine ballistic missile in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang on April 24, 2016. KCNA/via REUTERS. ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THIS IMAGE. SOUTH KOREA OUT. TPX IMAGES OF THE DAY - RTX2BDTMExpand / Collapse
North Korean leader Kim Jong Un guides on the spot the underwater test-fire of strategic submarine ballistic missile in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang. (KCNA/via REUTERS - FILE)
North Korea has warned it was considering a plan to launch four ballistic missiles to land in the sea just outside Guam.

Asked how the U.S. would respond, Mattis initially declined to say. When pressed, he said that if U.S. radars and other detection and tracking systems determine that a missile was going to fall into the sea, short of Guam, then the matter would be taken to President Donald Trump for a decision on how to respond.