FILE PHOTO: U.S. Secretary of Defence Jim Mattis leaves a news conference after a NATO defence ministers meeting at the Alliance headquarters in Brussels, Belgium June 29, 2017. REUTERS/Eric Vidal

WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Monday that if North Korea was to fire a missile at the United States, the situation could escalate into war.

“If they fire at the United States, it could escalate into war very quickly,” Mattis told reporters.

Mattis said the United States would know the trajectory of a North Korean missile “within moments” and if a missile is assessed to be hitting Guam, “we will take it out.”