North Korea on Friday accused the US and South Korea of attempting to assassinate its leader Kim Jong-un with a "bio-chemical substance".
In a report, North Korean state news agency KCNA said a "terrorist group" conspired with the CIA and South Korea's Intelligence Service (IS) to "commit bomb terrorism targeting the supreme leadership".
The report claimed a North Korean citizen was involved in the plot, using "biochemical substances, including radioactive substance and nano poisonous substance" to target Kim.
It also claimed the plot was "recently uncovered and smashed", and accused members of the CIA and IS of working with the North Korean citizen to provide money and weapons to carry out "state-sponsored terrorism", CNN reported.
A statement by the North Korean Ministry of State Security said that Pyongyang would find and "mercilessly destroy" the terrorists.
The ministry claimed that the North Korean man had been "corrupted and bribed" by South Korean intelligence services while he was working in Russia.
It listed several alleged payments made to him, amounting in total to nearly $300,000, according to the report.
A similar charge was laid against Pyongyang by Seoul in February following the murder of Kim Jong-Nam, allegedly at the hands of North Korean agents.
The half-brother of Kim Jong-un was poisoned with the VX nerve agent at Kuala Lumpur airport and died en route to a hospital.
North Korea repeatedly denied any involvement in Kim's death.