Defiant Donald Trump has warned Kim Jong Un's government to "get their act together" or face extraordinary trouble - suggesting he had been too mild when he vowed to unleash "fire and fury" on North Korea if it continued to threaten the US.
"Maybe that statement wasn't tough enough," the US president said, firing the latest salvo in the escalating exchange of threats between the nuclear-armed nations.
There was no obvious march towards combat, a day afterNorth Korea laid out plans to strike near the US island territory and major military hub of Guam, despite the angry rhetoric from both sides, but the stage is set for new confrontation.
The US and South Korean military plans to move ahead with large-scale exercises later this month that North Korea, now finalising plans to launch missiles towards Guam, claims are a rehearsal for war.
The exercises are an annual event, but come as Pyongyang says it is readying a plan to fire off four Hwasong-12 missiles in Guam's direction.
It would be sent to leader Kim Jong Un for approval just before or as the US-South Korea exercises begin.
Guam lies about 2,100 miles from the Korean Peninsula, and it is extremely unlikely Kim's government would risk annihilation with a pre-emptive attack on US citizens.
It is also unclear how reliable North Korea's missiles would be against such a distant target, given that its military has struggled to target effectively in the past.
The war games, called Ulchi-Freedom Guardian, are expected to run from August 21-31 and involve tens of thousands of American and South Korean troops on the ground and in the sea and air.
Washington and Seoul say the exercises are defensive in nature and crucial to maintaining a deterrent against North Korean aggression.
They were scheduled well before tensions began to rise over Mr Trump's increasingly fiery rhetoric and North Korea's announcement of the missile plan, which would be its most provocative launch yet.
Mr Trump declined to say whether the US was considering a pre-emptive military strike as he spoke to reporters before a briefing with his national security advisers at his New Jersey golf resort, but said the North had been "getting away with a tragedy that can't be allowed".
"North Korea better get their act together, or they are going to be in trouble like few nations have ever been in trouble," Mr Trump said, flanked by US vice president Mike Pence.
Accusing his predecessors of insufficient action, Mr Trump said it was time somebody stood up to the pariah communist nation.
Though tensions have been building for months amid new missile tests by the North, the pace has intensified since Saturday, when the United Nations Security Council passed sweeping new sanctions Mr Trump had requested.
After the North announced its plans to aim missile tests near Guam - home to about 7,000 troops and 160,000 people - US allies Japan and South Korea quickly vowed a strong reaction if it followed through.
Mr Trump echoed that threat on Thursday, insisting if North Korea took any steps to attack Guam, Pyongyang's leaders would have reason to be nervous.
"Things will happen to them like they never thought possible, OK?" he said.
He also said he would soon announce a request for a budget increase of "billions of dollars" for anti-missile systems.
Military activity on the Korean Peninsula will rise in any case because of the US-South Korean exercises.
Officials in Seoul confirmed on Friday that they are expected to begin without any delays, but refused to provide further details.
North Korea conducted its fifth nuclear test just days after last year's Ulchi-Freedom Guardian exercises concluded.
While tensions typically spike around the dates of the exercises, the situation generally calms afterwards.
But the heightened military activity is a concern this time because it could increase the possibility of a mishap or an overreaction of some sort by either side that could spin into a more serious escalation.
That possibility is made even more acute by the lack of any means of official communication across the Demilitarised Zone.
North Korea has been increasingly sensitive to the exercises lately because they reportedly include training for "decapitation strikes" to kill Kim Jong Un and his top lieutenants.
Pyongyang is also switching its propaganda machine into high gear by bringing in a large number of foreign journalists to ensure it gets global attention for an event next week in honour of its ruling Kim family on Mount Paektu, a dormant volcano that straddles the Chinese border and is something of a spiritual home for the regime.
Current and former US officials said if war did come, America and its allies would be likely to hit hard and fast, using air strikes, drone operations and cyber attacks aimed at military bases, missile sites, artillery, communications, command and control headquarters and intelligence gathering and surveillance capabilities.
US defence secretary Jim Mattis said on Thursday that while it was his responsibility to have military options, the US effort was focused on diplomacy and the Trump administration was working with its allies on a diplomatic solution.