South Korean president Park Geun-hye has said her country would respond "sternly and mercilessly" if provoked by North Korea.
Park's remarks have come amid tensions in the Korean peninsula over the latest purge by North Korean leader Kim Jong-un.
During her visit to one of the military installations in the border separating the two Koreas, the South Korean president said: "As we all know, the situation and security conditions on the Korean peninsula are very grave. North Korea's internal situation is ominous and therefore, concerns are growing that the North could attempt provocations."
Insisting that the South Korean commanders are capable of responding to any provocative tactics from Pyongyang, she said: "The best way to prevent North Korean provocations is to establish watertight security readiness to make [North Korea] not dare think of launching provocations. However, if [the North Korea] does launch provocations, we should deal sternly and mercilessly with them."
Both Seoul and Washington have expressed concern over the increasing tensions in North Korea following the execution of Kim's once-powerful uncle Jang Song-thaek.
Intelligence agencies in Seoul have warned that Pyongyang may resort to belligerent moves against South Korea in the near future apart from preparing for its controversial fourth nuclear test.
These have prompted South Korean ministries and troops to be placed on high alert.
Meanwhile, in North Korea, Kim is said to have visited the mausoleum of his father Kim Jong-il to pay homage, the state-run news agency reported.