SEOUL, South Korea -- North Korea on Friday accused the U.S. and South Korean spy agencies of an unsuccessful assassination attempt on leader Kim Jong Un involving bio-chemical weapons.

In a statement carried on state media, North Korea's Ministry of State Security said it will "ferret out and mercilessly destroy" the "terrorists" in the CIA and South Korean intelligence agency for targeting its supreme leadership.

North Korea frequently lambasts the United States and South Korea, but its accusation Friday was unusual in its detail.

The ministry said the spy agencies in June 2014 "ideologically corrupted and bribed" a North Korean citizen who had been working in Russia to carry out the alleged assassination on Kim after returning home.

It said South Korean agents gave money and satellite communication equipment to the North Korean to attack Kim during a public event with a bio-chemical weapon, such as a delayed-action radioactive or "nano poisonous" substance.

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The ministry said after a series of contacts and payments, the agents told the North Korean last month that the type of bio-chemical substance had been decided and that it would be supplied by the CIA.

The statement said in response to the alleged plot, a "Korean-style anti-terrorist attack will be commenced from this moment to sweep away the intelligence and plot-breeding organizations of the U.S. imperialists and the puppet clique," referring to South Korea.

Officials at South Korea's National Intelligence Service did not answer repeated phone calls seeking comment.

The North Korean statement comes during a period of tension on the Korean Peninsula over concerns that the North is preparing another nuclear test or missile launch, including a possible test of an intercontinental ballistic missile. Such moves would be a step toward the country's goal of developing nuclear-armed missiles capable of reaching the U.S. mainland.

Earlier this year, North Korea was accused of using the chemical war agent VX to assassinate Kim's exiled half brother at Kuala Lumpur's airport, which led to calls in the United States to relist the North as a state sponsor of terrorism.