Kim Jong-Un visits a rocket launching site in North Korea
North Korea's official Rodong Sinmun newspaper made the nuclear threat after the US ordered the deployment of a US Navy strike group to the waters off the Korean peninsula.
"Our revolutionary strong army is keenly watching every move by enemy elements with our nuclear sight focused on the US invasionary bases not only in South Korea and the Pacific operation theatre but also in the US mainland," it said.
White House spokesman Sean Spicer said Donald Trump had put North Korea "clearly on notice" but dismissed Pyongyang's nuclear attack threat.
"I think there is no evidence that North Korea has that capability at this time," he said. "Threatening something that you don't have the capability of isn't really a threat."
Donald Trump has declared that the US is sending an “armada” – including an aircraft carrier and submarines – towards North Korea in a show of force.
The extent of North Korea’s nuclear capabilities is shrouded in mystery because Kim Jong-un’s regime is so secretive and isolated from the rest of the world.
Although North Korea is not targeting the UK, there mounting concerns that North Korea could soon pose a nuclear threat to America’s west coast.
The police state is known to be accelerating its nuclear testing as well as increasing its nuclear weapons capabilities. North Korea carried out two nuclear tests last year.
It is believed that the North Korea is testing technology which would enable it to launch long-range missiles capable of targeting the US.
Dennis Wilder, former special assistant to George W Bush, warned that North Korea is developing a long-range intercontinental ballistic missile capable of reaching the US west coast.
"Such a move would be disastrous, after all a 10-kiloton weapon could kill 100,000 people," he told ABC’s Lateline.
"We believe, and American intelligence estimates say this, that the North Koreans could have such a weapon within the next four years.
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“In other words, during the term of President Trump."
But the acting US ambassador to Australia voiced “extreme concern” that North Korea will be able to strike the west coast of the US and Australia with nuclear missiles within two years.
James Carouso told The Australian yesterday: “They’ve gone from using these tests to get attention to now really making these tests to do tests. The question has been: what do we want to do about it.”
Secretive images revealed as North Korea prepares for war
Wed, April 5, 2017
A look at North Korea's firepower as it pursues its nuclear and ballistic missile programs in defiance of the United States and its allies.
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People watch a television news showing file footage of a North Korean missile launch, at a railway station in Seoul
North Korea has doubled the size of its facility for enriching uranium in recent years, according to Yukiya Amano, director general of the International Atomic Energy Agency.
The Institute for Science and International Security estimated that North Korea had 10 to 16 nuclear weapons at the end of 2014 but added four to six more before summer 2016.
A report from the institute said: “As of June 2016, North Korea has about 13-21 nuclear weapons, where one weapon was subtracted to reflect the underground test in early 2016.
“The upper bound, or 21 weapons, is greater in fact because it does not include the effect of any weapon-grade uranium produced in a possible second centrifuge plant.
“Nonetheless, this estimate, despite not being comprehensive, shows that North Korea appears to be significantly increasing its nuclear weapons capabilities.”