Defense Minister Han Min-koo on Wednesday urged the military to maintain a state of heightened readiness against possible North Korean provocations during President Park Geun-hye's overseas trip this week.

Park left for a two-nation visit earlier in the day, which will take her to Washington for the Nuclear Security Summit as well as Mexico where bilateral talks are planned. Park is scheduled to return home next week.

Han "called for thorough military preparedness during the president's state visit," ministry spokesman Moon Sang-gyun said. 

"While maintaining a heightened alert posture, all military units should be mentally and physically ready to complete their missions," the defense chief was quoted as saying.

South Korea is on unusually high alert against North Korean military provocations since the communist country ratcheted up its bellicose rhetoric over an ongoing joint military exercise between Seoul and Washington.

North Korea threatened to engulf Cheong Wa Dae, the presidential office-cum-residence, into a sea of fire last week as it continued to mount military threats. (Yonhap)