Kang Sam-hyon, the hermit state's ambassador to Iran, believes the CIA and South Korea's intelligence agency have both tried to kill Kim.
He said Washington and Seoul "hatched a vicious plot" to poison the tyrant when he attended a military parade in Pyongyang three years ago.
The envoy branded also accused the "evil" nations of preparing to commit terror in a bid to eliminate Kim.
Kang said: "The CIA of the US and the intelligence service of South Korea, hotbed of evils in the world, hatched a vicious plot to hurt the supreme leadership of the DPRK.
"Those acts have been put into the extremely serious phase of implementation after crossing the threshold of the DPRK.
"Their preparations to commit state-sponsored terrorism against the supreme leadership of the DPRK by use of a chemical substance has recently been detected."
North Korea claims the US and South Korea tried to kill Kim Jong-un
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Photographer Eric Lafforgue ventured to North Korea six times. Thanks to digital memory cards, he was able to save photos that was forbidden to take inside the segregated state
Eric Lafforgue/Exclusivepix Medi
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Taking pictures in the DMZ is easy, but if you come too close to the soldiers, they stop you
Speaking to Iranian state media, he claimed the spooks hired a lumberjack to carry out the alleged hit.
Kang claimed the man was paid £159,000 on two occasions from the intelligence agencies.
They allegedly plotted to poison the tyrant at a military parade
The US has threatened the DPRK with nukes for many years
The envoy's shocking claims will further ramp up tensions between the countires amid fears of Pyongyang carrying out a sixth nuclear test.
Kang blamed Washington for the escalating tensions, saying: "The US has threatened the DPRK with nukes for many years."
And he urged US President Donald Trump to stop playing "military games with South Korea" and instead strike a peace deal with North Korea.
The claims will ramp up tensions between the US and North Korea
Last month it was reported a crack US Navy Seal squad is preparing to take out Kim.
Seal Team Six is said to be carrying out secretive drills in South Korea simulating the dictator's assassination.
The same squad was behind the killing of evil al-Qaeda leader Osama bin Laden in Pakistan in 2011.