Kim Yo Jong, the influential sister of North Korean leader Kim Jong Un, advised the president of South Korea to "shut his mouth" after he underlined that his nation was ready to offer economic assistance in exchange for nuclear disarmament on Friday.

Her remarks indicate the first direct response from a senior North Korean official to what South Korean President Yoon Suk-yeol has called a "audacious" plan. 

The plan was first put forth in May, and Yoon Suk-yeol discussed it once more on Wednesday during a press conference to commemorate his first 100 days in office.

Yoon's belief that he could exchange economic cooperation for the North's honor and nuclear weapons was described as "really simple and still childish" by Kim Yo Jong in a statement published by the state news agency KCNA. 

Kim Yo Jong stated, "It would have been better for his image if he had kept his lips shut instead of speaking gibberish because he had nothing better to say."

The North's liaison in South Korea, the Minister for Unification, referred to Kim's remarks as "extremely rude and indecent."

Yoon has advocated for strengthening South Korea's military deterrence against North Korea even though he has stated his willingness to offer North Korea gradual economic help in exchange for the latter's halting nuclear weapons development and starting the process of denuclearization. 

Joint exercises between South Korea and the US have resumed after being long postponed. Important field exercises will start the following week.

Wednesday's joint drills, according to Kim, prove that the partners' rhetoric of diplomacy is hollow, notwithstanding what a spokesman for the U.S. State Department said about Washington's support for Yoon's policies.

In recent years, Kim Yo Jong has been an outspoken opponent of South Korea, viewed by some observers as the "bad cop" to her brother's more muted pronouncements.

The statement she released on Friday is her harshest personal attack on Yoon to date, but earlier this month she also published a foul-mouthed tirade in which she accused the South of being responsible for an outbreak of COVID-19 in the North and threatened "deadly retaliation" if there were any more incidents.

According to experts, South Korea's most recent economic strategy is comparable to ideas put out by earlier leaders, such as those made during meetings between Kim Jong Un and former United States President Donald Trump.