The detainee, Ko Hyon Chol, apologized for a crime he called "unforgivable", although South Korea's National Intelligence Service said it had no relation to the case. The tensions mainly stem from North Korea's pursuit of nuclear and missile development programmes in defiance of worldwide warnings.
"They hatched a plot of letting human scum Kim commit bomb terrorism targeting the supreme leadership during events at the Kumsusan Palace of the Sun and at military parade and public procession after his return home", KCNA said.
"Only the Central Intelligence Agency can produce such substance", it said, adding that South Korea had borne the funding. It refers to another of $50,000 but it is unclear if this is additional.
It lists several alleged payments made to him, amounting in total to almost $300,000, and says on his return to Pyongyang he was instructed to provide detailed information about a frequently used event ground and to assess possible methods of attack.
The dictatorship's security ministry said it would take vengeance against the countries.
It alleged that the citizen, named Kim, was given $290,000 over the course of various meetings, meant for himself and "terrorist accomplices", as well as satellite communications equipment.
"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".
Kim Jong-nam was killed at Kuala Lumpur International Airport on February 13 after two Asian women rubbed what the Malay police later said was nerve agent VX on Kim's face.
"Due to the US military provocations that are becoming more explicit day by day, the situation in the Korean peninsula that is already sensitive is being driven to a point close to nuclear war", a North Korean news anchor warned via the media as per a Reuters translation.
North Korea, in response, has increased its missile tests and even hinted at a new nuclear test in the coming weeks.
North Korea has continued on with its missile tests despite condemnation from the worldwide community and threats from the USA and its allies. The Trump administration has repeatedly warned "all options are on the table" regarding North Korea.
In a recent interview with Bloomberg that received some criticism, Trump said he'd be "honored" to meet with Kim Jong-un "under the right circumstances".
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