Kim Yo-jong is officially First Deputy Director of the Propaganda and Agitation Department but is thought to be de facto chief of staff and has become more prominent in North Korea in recent months. Ms Kim described the defectors as "human scum" and "rubbish-like mongrel dogs" for betraying Pyongyang according to Korean Central News Agency, the state press bureau. Responding to her intervention, a spokesperson for Seoul’s Ministry of Unification called for the leaflet operation to stop.
Ms Kim threatened that North Korea would back out of a 2018 military agreement and shut down a cross-border liaison office.
However, as talks between her brother and Donald Trump came to a standstill several parts of the agreement to ease border tensions has not yet been acted on.
Pyongyang has continued to test missiles, with several being fired in the direction of Japan.
The coronavirus pandemic has resulted in the liaison office suspending operations.
Kim Yo-jong is the younger sister of Kim Jong-un
Mrs Kim passing on condelescenes following the death of a former South Korean First Lady
Ms Kim warned: "If such an act of evil intention committed before our eyes is left to take its own course under the pretext of 'freedom of individuals' and 'freedom of expression', the South Korean authorities must face the worst phase shortly.”
No specific individuals were mentioned in the KCNA report.
Two winners in the South Korean legislative elections in April are likely to be of interest to Pyongyang.
Thae Yong-ho, the former North Korean deputy ambassador to the UK, took a seat in the National Assembly representing Gangnam.
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A viewpoint from the DMZ looking into North Korea
Mr Thae is part of the conservative United Future Party.
He defected in 2016.
Cho Myung-chul has been in the assembly since 2012.
Ahead of his victory, Mr Thae said he hoped his running would send a message back to the ruling elite of North Korea.
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Thae Yong-ho was deputy North Korean ambassador to the UK
Mr Thae celebrates winning a seat to the South Korean Parliament
He said: "I want to tell them that there is a new way for their future.”
Mr Thae said his defection was as a result of him becoming increasingly aware of the “gruesome realities” of life in North Korea.
He is the highest-ranking official to defect.
The history of North Korea missile tests
With reports circulating of her brother’s death, Ms Kim was touted as the future Supreme Leader of North Korea.
The Kim family has been ruling North Korea since the nation’s foundation after the Second World War.
It was their grandfather Kim Il-Sung who became the first supreme leader.
Ms Kim threatened to pull out of an agreement her brother made with President Moon
In March 2019, Ms Kim won a seat at the Supreme People’s Assembly.
Her brother did not stand, but previously represented the 111th Paektusan.
The siblings are thought to have grown close whilst at school in Switzerland.