Seoul (AFP) - North Korea on Friday accused the CIA of plotting with South Korea to assassinate leader Kim Jong-Un, amid soaring tensions in the flashpoint region.

The CIA and Seoul's Intelligence Services have "hatched a vicious plot" involving unspecified "biochemical substances" to kill the hermit state's young leader during public ceremonial events in Pyongyang, the Ministry of State Security said.

For the CIA "assassination by use of biochemical substances including radioactive substance and nano poisonous substance is the best method that does not require access to the target, their lethal results will appear after six or twelve months," the Ministry said in a statement carried by state media.

The accusation comes as Pyongyang issues increasingly belligerent rhetoric in a tense stand off with the administration of US President Donald Trump over its rogue weapons programme.

The war of words between the West and the reclusive regime has spiked in recent weeks, and Pyongyang has threatened to carry out a sixth nuclear test that would further inflame tensions.

The CIA and Seoul's Intelligence Services (IS) have "ideologically corrupted and bribed a DPRK citizen surnamed Kim" to carry out the attack on Jong-Un, the statement said.

"We will ferret out and mercilessly destroy to the last one the terrorists of the US CIA and the puppet IS of South Korea," the statement said, adding that the plot was tantamount to "the declaration of a war".

"The heinous crime, which was recently uncovered and smashed in the DPRK, is a kind of terrorism against not only the DPRK but the justice and conscience of humankind and an act of mangling the future of humankind."

The statement did not give any information on how the plot was foiled or what happened to the alleged spy.

North Korea maintains extensive surveillance operations over its own population, and open dissent against the regime is considered extremely difficult.