North Korea said it has issued a standing order for the execution of former South Korean President Park Geun-hye and her spy chief for what it said was a plot to assassinate its leader, and it demanded that the South hand the pair over.The North's official Korean Central News Agency (KCNA) said on Thursday "revelation showed" Park had masterminded a plot to execute its "supreme leadership" - North Korean leader Kim Jong-un - in 2015 and it was imposing the "death penalty on traitor Park Geun-hye" and her spy chief Lee Byung-ho.KCNA did not disclose the source of the "revelation" but a Japanese newspaper reported this week that Park approved a plan in 2015 to overturn the North Korean regime of leader Kim Jong Un. Park was ousted in March over a corruption scandal and is in detention in South Korea while on trial.South Korea's National Intelligence Agency (NIS) said it was "unpardonable" that North Korea made threats against its citizens and said the news report of a plot to kill Kim Jong Un "had no grounds.""We declare at home and abroad that we will impose the death penalty on traitor Park Geun-hye and ex-director of the puppet intelligence service ... criminals of hideous state-sponsored terrorism who hatched and pressed for the heinous plot to hurt the supreme leadership of the DPRK," KCNA said."We declare that in case the US and the South Korean puppet forces again attempt at hideous state-sponsored terrorism targeting the supreme leadership ... we will impose summary punishment without advance notice."KCNA said the statement was issued jointly by the North's Ministry of State Security, the Ministry of People's Security and the Central Public Prosecutors Office.READ MORE: North Korea and mounting tensions - The view from Seoul The NIS responded by dismissing Pyongyang's message as "groundless," insisting Seoul will not tolerate threats against its citizens, according to local news agency Yonhap.In May, North Korea accused the U.S. Central Intelligence Agency and the South's spy agency of another plot to assassinate its "supreme leadership" with biochemical weapon.At that time, it also demanded the handover of former NIS chief Lee. South Korea's ousted president is currently facing a corruption trial over a scandal that ignited mass protests and led to her downfall.There are 18 charges against Park, the country's first democratically elected leader to be removed from office, including extortion, bribery and abuse of power.She could be imprisoned for life if convicted.