Kim Jong Un has threatened the US with a "super-mighty preemptive strike" and warned America: "Don't mess with us".
State controlled media claimed North Korea could "immediately wipe out the US mainland" and reduce its enemies "to ashes".
The latest threat from Pyongyang comes amid mounting tensions between North Korea and America and after China moved 150,000 troops to its border with the secretive state, according to Daily Mail.
This morning it emerged that Vladimir Putin is also reinforcing his border with North Korea by relocating troops and equipment.
Video purports to show one of three trains loaded with military equipment moving towards the 11 mile-long land frontier between Russia and the repressive state in Russia's far south east.
Another clip highlights military helicopter movements towards the North Korean border and manoeuvres across rough terrain by army combat vehicles. Other reports suggest there have been military moves by road as well.
There have been concerns that if a conflict breaks out Russia could face a humanitarian exodus from North Korea.
But Putin has been warned, too, that in the event of a US strike on Kim Jong-un's nuclear facilities, contamination could swiftly reach Russia.
"Railway trains loaded with military equipment moving towards Primorsky region via Khabarovsk have been noticed by locals," reported primemedia.ru in the Russian far East - linking the development to the North Korean crisis.
"The movement of military equipment by different means of transport to southern areas is being observed across Primorsky region over the past week," said military veteran Stanislva Sinitsyn.
"Many relate this to the situation in the Korean peninsula.
"The video shows artillery systems that either support troops in assault or meet the aggressor."
He said: "The movement of military equipment means that authorities of our country are keeping up with the situation - and take appropriate measures."
"If the situation worsens, especially related to military events, the armed forces of all the neighbouring countries obviously monitor it more closely, and we are no exception.
"It is not the first time that North Korea has broken the peace in the region, that's why this situation deserves attention."
Russian military spokesman Alexander Gordeyev declined to give the exact reasons for the troop and equipment movements but said exercises had recently ended in the TransBaikal region of Siberia.
However, a number of local sources appear to believe the movements are linked to the Korean crisis.
The naval port of Vladivostok, where Russia has huge military forces, is less than 160 kilometres miles from North Korea.
Expert on the repressive state, Konstantin Asmolov, said: "Should the US strike with missiles at North Korea's nuclear facilities, a radioactive cloud will reach Vladivostok within two hours."
Asmolov, from the Russian Far Eastern Institute, warned that in the event of full-scale war "hungry asylum seekers will flood into Russia."
Russia on Wednesday blocked UN Security Council condemnation of Pyongyang's latest missile test, even though China, which has a major frontier with North Korea had backed the strongly-worded statement put forward by the United States.
The proposed statement would have demanded that North Korea "conduct no further nuclear tests" and halt missile launches.
Pyongyang carried out a failed test on Sunday.
Russia wanted to include language contained in a previous statement stressing the need to achieve a solution through dialogue, according to council diplomats.
Moscow's deputy foreign minister Sergei Ryabkov said: "Unfortunately, we have to admit that the risk of a serious conflict in this region has substantially increased."
He called for a "demonstration of responsibility" from all sides to avoid escalation.
U.S. President Donald Trump, meanwhile, has taken a hard line with North Korean leader Kim Jong Un, who has rebuffed admonitions from sole major ally China and proceeded with nuclear and missile programmes in defiance of U.N. Security Council sanctions.
There has been some confusion over the whereabouts of a US aircraft carrier group after Trump said last week he had sent an "armada" as a warning to North Korea, even as the ships were still far from Korean waters.
The U.S. military's Pacific Command explained that the USS Carl Vinson strike group first had to complete a shorter-than-planned period of training with Australia. It was now heading for the Western Pacific as ordered, it said.
China's influential Global Times newspaper, which is published by the People's Daily, the Communist Party's official paper, wondered whether the confusion was deliberate.
"The truth seems to be that the U.S. military and president jointly created fake news and it is without doubt a rare scandal in U.S. history, which will be bound to cripple Trump's and US dignity," it said.
North Korea did not refer to the mix-up but said the United States and its allies "should not mess with us".
The Rodong Sinmun, the official newspaper of the North's ruling Workers' Party, did not mince its words.
"In the case of our super-mighty preemptive strike being launched, it will completely and immediately wipe out not only U.S. imperialists' invasion forces in South Korea and its surrounding areas but the U.S. mainland and reduce them to ashes," it said.
On Thursday, footage emerged of Kim Jong Un smiling and waving as cheering crowds watched a simulation of a US city being wiped out by a nuclear attack.
North Korea put on a musical show to mark the birthday of founding father Kim Il Sung which ended with a mock-up of rockets engulfing America in flames.
The choral performance was attended by dictator Kim Jong-un, the elder of Kim's grandson, on Sunday, after a massive military parade in the capital.
The singing was followed by footage of its test-firing of a missile in February which, in the video, was joined by other missiles shooting into sky, passing over the Pacific and exploding in giant balls of flames in the United States.
The video ended with a picture of the American flag in flames, overlapping row after row of white crosses in a cemetery.
'When the performance was over, all the performers and participants in the military parade broke into enthusiastic cheers of "hurrah!", state run KCNA news agency said.
State TV footage showed leader Kim smiling and waving in return.
"The Dear Supreme Leader waved back to them and congratulated the artistes on their successful performance," KCNA said.
North Korea said in February that it had successfully tested a new type of medium- to long-range ballistic missile, the Pukguksong-2, propelled by a solid-fuel engine.
During Saturday's military parade it displayed what appeared to be new intercontinental ballistic missiles.
And a day later it conducted a failed missile test, which drew international condemnation.
North Korea regularly threatens to destroy the United States and amid heightened tension on the Korean peninsula, it has escalated a war of words, warning of full-out nuclear war if Washington takes military action against it.
US Vice President Mike Pence, on a trip to Asia, has repeatedly warned that the "era of strategic patience" with North Korea is over and on Wednesday said it would meet any attack with an "overwhelming response".