Washington, Aug 15 (IANS): US Secretary of Defense Jim Mattis has warned that if North Korea fires at the US, the situation could quickly escalate into war, the media reported on Tuesday.

"If they (North Korea) fire at the US, it could escalate into war very quickly," Xinhua news agency quoted Mattis as saying on Monday.

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

According to Mattis, the Pentagon would know "within moments" if a missile launched by North Korea was headed for US territory, including Guam.

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

If a missile is fired in the direction of Guam but not hit the US territory, Mattis said: "It becomes an issue we take up however the President chooses."

A North Korean military statement on Thursday said its plan to strike Guam with intermediate missiles would be ready by mid-August and its implementation would depend on a decision by the Communist nation's top leader Kim Jong Un.

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