The United States has been secretly engaged in an attempt at back channel diplomacy with North Korea for months despite the increasingly bellicose public rhetoric between Washington and Pyongyang.
In the latest round of escalating threats President Donald Trump said the US military was "locked and loaded" while Kim Jong-un, the North Korean leader, accused him of "driving the Korean peninsula to the brink of nuclear war". Other nations, including Russia and China, called for calm.
In a tweet issued from his golf course in New Jersey, Mr Trump said: "Military solutions are now fully in place, locked and loaded, should North Korea act unwisely. Hopefully Kim Jong-un will find another path!"
The term "locked and loaded" was popularised in the 1949 war film "Sands of Iwo Jima" starring John Wayne.
He later said that Mr Kim "will regret it fast" if he continues his threats to US territories and allies.
Mr Trump said he hoped North Korea "fully" understood the gravity of his words, warning Pyongyang against taking any military action against the US or its allies.
"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. "Those words are very easy to understand."
The other path Mr Trump mentioned in his tweet may have been a reference to a senior US diplomat who has been engaged in back-channel diplomacy.
There have been regular contacts between Joseph Yun, the US envoy for North Korea policy, and Pak Song Il, a senior North Korean diplomat, at Pyongyang's UN mission.
It is known as the "New York channel" as the two men met in that city, and could form the foundation for any future negotiations.
It was Mr Yun who went to Pyongyang in June to discuss the release of Otto Warmbier, the 22-year-old US student imprisoned in North Korea. Warmbier returned in a coma and suffering brain damage, and died soon after his return to the US. He is the only US diplomat in contact with any North Korean counterpart.
Rex Tillerson, the US secretary of state, hinted at the potential route for dialogue last week when he said: "We have other means of communication open to them, to certainly hear from them if they have a desire to want to talk."
China said it would "prevent" a pre-emptive strike by the US on its neighbour.
The state-run Global Times newspaper said: "China should make clear that if North Korea launches missiles that threaten US soil first, and the US retaliates, China will stay neutral.
"If the US and South Korea carry out strikes and try to overthrow the North Korean regime, and change the political pattern of the Korean Peninsula, China will prevent them from doing so."
Sergei Lavrov, Russia's foreign minister, said Moscow was deeply worried and considered the risk of military conflict between the US and North Korea "very high".
He again suggested a plan under which North Korea would halt missile tests if the US and South Korea would stop large-scale military exercises.
He said: "Unfortunately, the rhetoric in Washington and Pyongyang is now starting to go over the top. We still hope and believe that common sense will prevail.
"When it comes close to fight the one who is stronger and wiser should be the first to step back from the brink." The Pentagon later confirmed that a huge annual joint exercise by the US and South Korea would go ahead as planned in 10 days' time.
Mr Trump has said he would not allow the hermit state to develop a nuclear weapon capable of hitting the US.
But Pyongyang's nuclear programme has advanced more rapidly than expected, with two intercontinental ballistic missile tests last month and intelligence reports alleging that N.Korea now has miniaturised its nuclear warheads, which extends the range of its missiles and potentially brings US targets into reach.
Earlier this week Mr Trump promised "fire and fury like the world has never seen" if North Korea threatened the US or its allies.
Pyongyang responded by saying it may fire four missiles to land off the coast of Guam, a US territory in the Pacific, within days.
A newspaper on Guam had "14 minutes" as its headline, referring to the time North Korean missiles would take to reach the island of 160,000 people.
The island's Homeland Security Department issued a warning to residents which said: "Do not look at the flash or fireball - it can blind you. Take cover behind anything that might offer protection."
Japan began deploying land-based Patriot surface-to-air interceptor missiles, including in Hiroshima, as North Korean missiles headed for Guam would pass over its airspace.
Earlier yesterday, China called on the US and North Korea to tone down their fiery rhetoric.
Geng Shuang, a foreign ministry spokesman, said both sides should avoid "going down the old path of alternately showing strength and continuously escalating the situation".
Mr Trump's top advisers also stressed yesterday that Washington would prefer a diplomatic solution.
Jim Mattis, US defence secretary, warned that war with North Korea would be "catastrophic" and said diplomatic efforts were yielding results.
"The American effort is diplomatically led, it has diplomatic traction, it is gaining diplomatic results and I want to stay right there right now," Mr Mattis said at an event in California.
"The tragedy of war is well-enough known it doesn't need another characterization beyond the fact that it would be catastrophic," he added.
North Korea's nuclear history: key moments
Angela Merkel, the German chancellor, said: "I don't see a military solution and I don't think it's called for. I think escalating the rhetoric is the wrong answer, I see the need for enduring work at the UN Security Council."
Malcolm Turnbull, the Australian leader, said his country was "joined at the hip" with the United States.
Mr Trump, who is on a 17-day "working holiday" in New Jersey, will make a brief day trip back to Washington on Monday, a White House official confirmed. The White House gave no reason for the change in his schedule.
The North Korean nuclear issue needs a peaceful resolution, Chinese President Xi Jinping told U.S. President Donald Trump in a telephone call on Saturday, and called on the "relevant side" to exercise restraint, state television said.
Mr Trump issued a new threat to North Korea on Friday, saying the U.S. military was "locked and loaded", as Pyongyang accused him of driving the Korean peninsula to the brink of nuclear war and world powers expressed alarm.
Mr Xi told Trump that it was in the joint interests of both China and the United States to achieve the denuclearisation of the Korean peninsula and protect peace and stability there, state television said in a brief report.
"The relevant side must at present exercise restraint, and avoid words and actions that exacerbate tensions on the Korean peninsula," the report paraphrased Mr Xi as saying.
Resolving the nuclear issue ultimately needs to be done politically via talks, and China is willing to maintain communication with the United States on the basis of mutual respect to push for an appropriate resolution, Xi added.
Chinese state television cited Mr Trump as telling Xi that he fully understands the role China has been playing on the North Korean nuclear issue.