In February, China suspended all imports of coal from North Korea as part of its effort to implement United Nations Security Council sanctions aimed at stopping the Pyongyang's nuclear weapons and ballistic-missile program.
The date of the alleged assassination attempt is unclear; however, Kim Jong Un presided over a military parade on April 15.
The allegations came after the US House of Representatives voted overwhelmingly in favour of imposing tighter sanctions on North Korea by targeting its shipping industry.
Although the North Korean suspect was not named in the official televised broadcast, he was identified by his surname - Kim.
The call came as the US House of Representatives on Thursday overwhelmingly voted in favor of broadening sanctions against North Korea, including efforts to cut the regime's sources of worldwide financing.More news: Padres pounded by Bellinger, lose 8-2 to Dodgers
Placing the level of pressure needed to force Kim Jong-un to give up his nuclear weapons program risks the North Korean regime collapsing, leading to refugee flows and potentially a unified Korea allied with the United States, he said.
It said "Kim" had been told that the best method was the use of "biochemical substances including radioactive substance and nano poisonous substance" whose results would "appear after six or 12 months".
It comes after Mr Kim's estranged half-brother Kim Jong-nam was killed at a Malaysian airport after he was sprayed with a deadly nerve agent. The South Korean border is in sight from these places, which makes the border area more vulnerable.
The alleged plot was a "hideous crime" the security ministry said, and tantamount to "the declaration of a war".
North Korea has also repeatedly accused the USA of plotting preemptive nuclear strikes on Pyongyang, practicing dropping nuclear bombs on North Korea with planes which aren't even capable of carrying nuclear devices, and planning a massive invasion of the North.More news: President Trump calls North Korean leader a 'pretty smart cookie'
Chinese state-run media have also called for harsher sanctions against the North in the event of a fresh atomic test, urging Pyongyang to "avoid making mistakes", and spoken of the need for it to abandon its nuclear programmes.
Last year, lawmakers said Seoul "has a general idea and plan to use precision missile capabilities to target the enemy's facilities in major areas as well as eliminating the enemy's leadership".
John Delury, a professor of worldwide relations at Yonsei University in Seoul, said one of the North Korean regime's main narratives is that the country faces relentless hostility from the outside world, driven by the United States.
The idea was to launch a bombing attack at a military parade attended by Kim, the North Korean statement said.More news: Qatar maintain Federation Internationale de Football Association rankings