WASHINGTON, Aug. 14 (Xinhua) -- U.S. Secretary of Defense Jim Mattis warned on Monday that if the Democratic People's Republic of Korea (DPRK) fires at the United States, the situation could quickly escalate into war.

"If they (DPRK) fire at the United States, it could escalate into war very quickly," Mattis told reporters.

"If they shoot at the United States, I'm assuming they hit the United States. If they do that, it's game on," he added.

According to Mattis, the Pentagon would know "within moments" if a missile launched by the DPRK was headed for U.S. territory, including Guam.

He said the U.S. military would "take it out" if a missile was headed for any U.S. territory.

If a missile is fired in the direction of Guam but not hit the U.S. territory, Mattis said, "it becomes an issue we take up however the president chooses."

The DPRK military said in a statement Thursday that its plan to strike Guam with intermediate missiles will be ready by mid-August and its implementation will depend on a decision by the DPRK's top leader Kim Jong Un.

It was a response to U.S. President Donald Trump's unusually stern warning to the DPRK on Tuesday, when he said "North Korea (DPRK) best not make any more threats to the United States. They will be met with fire and fury like the world has never seen."