Lee has sharpened his language against the DPRK after coming under pressure over a perceived weak response to two DPRK attacks this year that raised tension on the peninsula to the highest level since the 1950-1953 Korean War.

The clashes have led some analysts to say the chance of a wider conflict is greater than ever.

In the latest rhetorical sparring, the DPRK last week threatened a nuclear "sacred war" and Lee vowed "a merciless counterattack" against any fresh DPRK attacks as rare large-scale military drills by the RoK kept tension high.

"We can't afford to have division of “you against me” in the face of national security, because what’s at stake is our very lives and the survival of this nation", Lee said in a national radio address.

Lee said it was divided public opinion after the DPRK attack on a RoK navy ship in March, in which 46 sailors were killed, that had prompted the DPRK to bombard a RoK island near a disputed sea border last month.

Lee took office in 2008 and ended a decade of free-flowing economic aid to the DPRK from his two liberal predecessors that persisted despite previous acts of violence against the South.