US President Donald Trump warned North Korean leader Kim Jong-Un not to take any action against the US, its territories including Guam or its allies, warning he would regret such a move - and "regret it fast".
Mr Trump said Washington was looking "very carefully" at its military options, and that he hoped Mr Kim had taken his words to heart in recent days.
Just this morning, Mr Trump said America's military was "locked and loaded".
North Korea has said it is readying plans to launch missiles towards the US Pacific territory of Guam.
"I hope that they are going to fully understand the gravity of what I said, and what I said is what I mean," Mr Trump told reporters.
"If he 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."
Military solutions are now fully in place,locked and loaded,should North Korea act unwisely. Hopefully Kim Jong Un will find another path!— Donald J. Trump (@realDonaldTrump) August 11, 2017
Pyongyang accused Mr Trump of driving the Korean peninsula to the brink of nuclear war and world powers expressed alarm.
The Pentagon said the United States and South Korea would proceed as planned with a joint military exercise in 10 days, an action sure to further antagonise North Korea.
Meanwhile, Russia, China and Germany voiced dismay at the escalating rhetoric from Pyongyang and Washington.
Mr Trump, on holidays at his New Jersey golf resort, kept up the war of words and again referenced North Korea's leader in his latest bellicose remarks toward Pyongyang this week.
"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely," he wrote on Twitter. "Hopefully Kim Jong Un will find another path!"
- North Korea crisis - what could happen next
- Trump doubles down on North Korean threats
- UN Security Council imposes new sanctions on North Korea
- Stocks, dollar extend slide as US-North Korea tensions intensify
The term 'locked and loaded', popularised in the 1949 war film Sands of Iwo Jima starring American actor John Wayne, refers to preparations for shooting a gun.
Asked later by reporters to explain the remark, "Those words are very, very easy to understand."
Again referring to Mr Kim, Mr Trump added: "If he utters one threat ... or if he 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."
Today's tweet by the Republican president, a wealthy businessman and former reality television personality, came after the North Korean state news agency, KCNA, put out a statement saying "Trump is driving the situation on the Korean peninsula to the brink of a nuclear war".
While the US president insists on ramping up the war of words, there is a decreasing chance of any diplomatic solution
Guam, the Pacific island that is a US territory, posted emergency guidelines today to help residents prepare for any potential nuclear attack after a threat from North Korea to fire missiles in its vicinity.
"Do not look at the flash or fireball … it can blind you," the guidelines stated. "Take cover behind anything that might offer protection."
Guam is home to a strategically located US air base, a navy installation, a coast guard group and roughly 6,000 US military personnel.
KCNA said yesterday the North Korean army would complete plans in mid-August to fire four intermediate-range missiles over Japan to land in the sea 30-40km from Guam.
The United States, which is technically still at war with North Korea after the 1950-53 Korean conflict ended with only a truce, wants to stop Pyongyang from developing nuclear missiles that could hit the United States.
North Korea, a reclusive nation with an underdeveloped economy and few allies, sees its nuclear arsenal as protection against the United States and its partners in Asia.