Last week's ballot saw Park's conservative Saenuri Party lose its parliamentary majority for the first time in 16 years, as voters registered their dissatisfaction with the her economic record and soaring youth unemployment.
The result handed the country's three centre-left opposition parties a combined 167 seats in the 300-seat legislature.
The crushing defeat left Park, who has less than two years left of her single, five-year term, a lame duck leader who will struggle to push through her reform agenda.
"Through the elections, the South Korean people placed a death sentence on the confrontational policies of the Park Geun-Hye forces that drove North-South relations to catastrophe," said a spokesman for the Committee for the Peaceful Reunification of Korea (CPRK).
The defeat left Park a "vegetable president" and one of the political "living dead," the spokesman said in a statement carried by the North's official KCNA news agency.
If Park felt any genuine remorse or responsibility for the defeat, she should "apologise a hundred times" to the people of South and North Korea and step down from her post, the statement said.