A North Korean official has warned "thermo-nuclear war may break out at any moment" and said Donald Trump's provocative tweets are adding fuel to a "vicious cycle" of tensions.
North Korea's vice foreign minister Han Song Ryol said that if the US shows any sign of "reckless" military aggression, Pyongyang is ready to launch a pre-emptive strike of its own.
He added that North Korea will keep building up its nuclear arsenal in "quality and quantity" and said Pyongyang is ready to go to war if that's what Trump wants.
Vice Minister Han said Pyongyang has determined the Trump administration is "more vicious and more aggressive" than that of Barack Obama.
Tensions between Pyongyang and Washington go back to President Harry Truman and the 1950-53 Korean War, which ended in an armistice, not a peace treaty. But the heat has been rising rapidly since Trump took office in January.
"Trump is always making provocations with his aggressive words," Han said. "It's not the DPRK but the US and Trump that makes trouble."
He added: "We will go to war if they choose."
A US State Department official said later Friday the US was aligning "all elements of national power" to get North Korea to abandon its nuclear and missile programs.
The official, who wasn't authorised to be quoted by name and demanded anonymity, lamented Pyongyang's "far too common and far too dangerous" provocations, and said Washington would work with international partners to cut the North's government off "from the rest of the world."
Han dismissed the suggestion Trump made last year during his presidential campaign that he was willing to meet Kim Jong Un, possibly over hamburgers.
"I think that was nothing more than lip service during the campaign to make himself more popular," Han said. "Now we are comparing Trump's policy toward the DPRK with the former administration's and we have concluded that it's becoming more vicious and more aggressive."
Han said North Korea changed its military strategy two years ago, when the reports of "decapitation strike" training began to really get attention, to stress pre-emptive actions.
"We've got a powerful nuclear deterrent already in our hands, and we certainly will not keep our arms crossed in the face of a US pre-emptive strike," he said. "Whatever comes from the US, we will cope with it. We are fully prepared to handle it."
North Korea's military said on Friday it would "ruthlessly ravage" the United States if Washington chose to attack, as a US aircraft carrier group headed for the region amid fears the North may conduct a sixth nuclear weapons test.
"Our toughest counteraction against the U.S. and its vassal forces will be taken in such a merciless manner as not to allow the aggressors to survive," North Korea's official KCNA news agency quoted its military as saying in a statement.
The Kremlin said on Friday it favored diplomatic methods of resolutions of all crises, including on the Korean peninsula, amid mounting tensions between Washington and Pyongyang over North Korea's nuclear program.
"We call all countries for restraint, we call all the countries to refrain from any actions that could amount to provocative steps", Kremlin spokesman Dmitry Peskov told a conference call with reporters.