In a 1,800-word report, the agency said that the plot involved a North Korean citizen and the use of "biochemical substances including radioactive substance and nano poisonous substance" to target Kim during a major event such as a military parade.
The North's Ministry of State Security released a statement saying the CIA and the National Intelligence Service (NIS) of South Korea "hatched a vicious plot to hurt the supreme leadership" of North Korea.
China, North Korea's largest trading partner and main benefactor, suspended imports of North Korean coal in line with United Nations sanctions earlier this year and has recently been urging its traditional ally to stop nuclear and missile activities amid USA pressure to use its leverage to resolve the nuclear standoff.
Earlier this year, Kim Jong-un's half brother, Kim Jong-nam, was killed with the banned nerve agent VX at Kuala Lumpur worldwide airport.
The North Korean Security Ministry alleged that a North Korean native working in Russian Federation as a lumberjack was "bribed", Yonhap reports, by the Central Intelligence Agency and NIS to kill Kim Jong-un.
North Korea has a history of bombastic propaganda featuring unfounded claims.
The report claimed that USA officials bribed the North Korean citizen, who it called "human scum", with $750,000 in payments to assassinate Kim using biochemical substances.
He said North Korea's aim could be to divert attention from the use of VX nerve gas to assassinate the estranged half-brother of Kim Jong Un at Malaysia's Kuala Lumpur International Airport in February, or to influence South Korea's May 9 election.
Ri Byong Ho, the North Korea head of intelligence, said the suspect was a "very important person" and that "there have already been more than 80 planned terrorist attacks" that have been foiled.
The North Korean article cited recent commentaries by Chinese state media that it said shifted the blame for deteriorating bilateral relations onto the North and raised "lame excuses for the base acts of dancing to the tune of the U.S".
During a visit to Jangjae and Mu islands, Kim reportedly "acquainted and examined the plan for fire strike of the newly organised forces at the objects of the enemy".
The accusations come amid a period of high tension in the region, as the Trump administration appears to be stepping up the pressure in response to the latest missile tests by North Korea.
On Friday, a spokesman for North Korea's Foreign Ministry called Gardner's remarks a "provocation that can not be overlooked" and an affront to the dignity of the country's supreme leadership, from a man who was "tantamount to mentally deranged".
"This has created a risky situation in which thermos-nuclear war may break out at any moment".