North Korean leader Kim Jong Un last December oversaw a military drill that involved a simulated attack on the Blue House, South Korea's presidential office and residence.
A statement from North Korea's official media announced the accusation and added that their government will "ferret out and mercilessly destroy" US and South Korean "terrorists" who purportedly targeted Kim.
The accusation was made Friday by North Korea's Ministry of State Security in a lengthy statement carried by the official Korean Central News Agency.
North Korean news agency KCNA said the alleged plot included the use of "biochemical substances including radioactive substance and nano poisonous substance".
"Korean-style anti-terrorist attack will be commenced from this moment to sweep away the intelligence and plot-breeding organizations of the USA imperialists and the puppet clique, the most mean and brutal ugly terrorist group in the world", the statement added.
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".
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. But longtime North Korea observers say that organized subversion is highly unlikely in the North's police state, where huge numbers of soldiers and security agents are dedicated to the sole task of protecting Kim.
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China said in mid-February that it will halt imports of North Korean coal in line with the UNSC sanctions against Pyongyang.
The U.S. and South Korea are installing a missile defense system and their two navies are staging joint military drills.
"To a certain extent, we are immune to North Korea's provocative actions over the years", said financial consultant Kim Min Ji, 27, who read about North Korea's failed missile test last Saturday in the news but did not bother with the details.
"(North Korea) will never beg for the maintenance of friendship with China, risking its nuclear program which is a precious as its own life, no matter how valuable the friendship is", the commentary continued.
Pyongyang claims the CIA and Seoul's Intelligence Services had "hatched a vicious plot" to kill the secretive state's young leader as he attended ceremonial events.
The visit was highly symbolic since the islets are near Yeonpyeong Island, which was the site of a deadly North Korean artillery attack in 2010 - one of the most serious incidents between the two countries since the Korean War ended in 1953.