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 biochemical 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 responsible 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 was 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 using a biochemical weapon such as a delayed-action radioactive or “nano poisonous” substance.

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

The statement, carried by North Korea’s official news agency and read on state TV, didn’t describe how the alleged plot was broken up or give the full name of the North Korean suspect, identifying him only by his surname, Kim, and didn’t say whether anyone else was in custody.

In Washington, the CIA declined to comment, and officials at South Korea’s National Intelligence Service did not answer repeated phone calls.