Speaking at a Cabinet meeting, Park warned South Korea's relations with the isolated Communist country could become more unstable due to the current environment, Yonhap News Agency reported.
"I think we are at a very important point in history," she said, warning the situation on the Korean Peninsula and in Northeast Asia is changing so rapidly her government cannot lower its guard against North Korean threats.
"North Korea is currently engaged in a reign of terror while carrying out massive purges in order to consolidate Kim Jong Un's power," she said.
In the latest purge in North Korea, Kim ousted his uncle, Jang Song Thaek from all his influential and powerful posts, accusing him of corruption and being involved in "anti-party" and "counter-revolutionary factional" activities.
North Korean state media showed Jang being arrested at a political bureau meeting of the ruling Workers Party.
Yonhap said Jang's ouster could affect North Korea's foreign policies as he was seen as a moderate figure in a regime dominated by hawkish military generals.
The development also comes as North Korea continues with its nuclear program despite tough U.N. sanctions. It conducted its third nuclear test last February. The six-nation talks on the North's nuclear disarmament remains stalled.