The president of the United States issued another stark warning to North Korea on Friday, saying that if it attacks the island of Guam or any other territory of the United States or of an ally, it will very soon regret it.

Pyongyang had said Thursday it was preparing a plan to fire two intermediate-range ballistic missiles that would fly over Japan and land near the territorial waters of the US Pacific territory of Guam - the location of a strategic US naval base.

"If he (North Korean leader Kim Jong-un) does anything with respect to Guam or any place else that's an American territory or an American ally, he will truly regret it and he will regret it fast," Trump said Friday in a brief statement to the press at his golf club in Bedminster, New Jersey.

Trump, who has spent days escalating the verbal back-and-forth with Kim, said he hopes the North Korean leader "fully understands the gravity of what I said" and added that the US is studying its military options "very carefully."

The president made those statements after being asked about a Twitter message he posted hours before with the phrase: "Military solutions are now fully in place, locked and loaded."

"I hope that they are going to fully understand the gravity of what I said, and what I said is what I mean. Those words are very, very easy to understand," he said.

"This man will not get away with what he's doing, believe me," Trump said about the North Korean leader's threat against Guam.

Asked about German Chancellor Angela Merkel's stand against a military solution for the North Korea conflict, Trump called her "a very good person," but said "let her speak for Germany...she's certainly not referring to the United States, that I can tell you."

About those who slam his harsh rhetoric against North Korea, which he threatened with "fire ando fury" if it continues its aggressive attitude, he hit back saying "If somebody else uttered the exact same words that I uttered they would say what a great statement, what a wonderful statement," and added that there are "tens of millions of people in this country that are so happy with what I am saying, because they're saying, finally, we have a president that's sticking up for our nation and frankly sticking up for our friends and our allies."

Despite Trump's tough talk, the White House and Pentagon denied Friday that there has been any change in America's military plans."