North Korea are in the midst of preparing missile attacks, US officials have claimed
Missile launchers have been spotted moving across the hermit kingdom alerting officials of potential nuclear activity.
This has triggered the US to ramp up their surveillance of North Korea, according to anonymous military sources.
Satellites, drones and other aircraft carriers have been used to monitor the region of Wonsan, within eastern North Korea.
Washington’s warning comes after a Pyongyang envoy said the nation is preparing a deadly “strike first” missile system as it continues to “accelerate” its nuclear weapon programme.
Choe Myong Nam, deputy ambassador at the North Korean mission to the United Nations in Geneva said the development of inter-continental ballistic missiles (ICBM), capable of striking the US, are being prioritised.
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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 news footage of a missile launch on a giant television screen outside the main railway station in Pyongyang on March 7, 2017
Despite warnings from Donald Trump’s administrations, Ms Nam said the hermit state is not afraid of being treated for more strictly than under Barack Obama’s presidency.
She added: “I think this is stemming from the visit by the Secretary of State [Rex Tillerson] to Japan, South Korea and China. We of course are not afraid of any act like that.
"Even prohibition of the international transactions system, the global financial system, this kind of thing is part of their system that will not frighten us or make any difference."
On Monday, White House press secretary Sean Spicer said America's "patience is over" with North Korea, in reaction to its latest rocket engine test on Sunday.
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North Korea developing an engine to test a powerful rocket
Speaking at a news briefing, Mr Spicer said there is “growing concern” about the nuclear capabilities of the rogue communist nation.