South Korean President Lee Myung-bak called for national solidarity on Monday against military aggression by the North, saying Pyongyang looks for division in the South as an opportunity to strike.
Lee has sharpened his language against the North after two attacks in 2010 that raised tension on the Korean peninsula to the highest since the 1950-53 Korean War, leading some analysts to say the chance of a wider conflict was now greater than ever.
In the latest rhetorical sparring, the North last week threatened a nuclear "sacred war" and Lee vowed "a merciless counterattack" against any fresh North Korean attacks as rare large-scale military drills in the South kept tensions 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 that it was divided public opinion in the wake of the North's submarine attack on one of South Korea's navy ships in March, killing 46 sailors, that had prompted Pyongyang to bombard a South Korean island near a disputed sea border in November. North Korea denies responsibility for the ship attack.
"It is when we show solidarity as one that the North dares not challenge us. Their will to challenge breaks," he said.
Lee took office in 2008 and ended a decade of free-flowing economic aid given to the impoverished neighbor by his two liberal predecessors despite acts of violence against the South.
But he has come under criticism for being indecisive and ineffective against the North's military acts. Critics have said that he has little to show for his hard line.
Analysts said that the frequency and severity of North Korea's provocations had pushed Lee against a political wall and he had little choice but to order a harsh retaliation against Pyongyang which could spark a wider military conflict.
Government researchers in Seoul say the North could attack five islands belonging to the South in the West Sea in 2011.
"There is a high possibility that the North's provocation linked to its succession will continue in various forms," the report by the Institute for National Security Strategy said.
"Competition in the military to express loyalty for successor Kim Jong-un will intensify, increasing instability and the possibility of sudden provocation against the South," the report released on Sunday said.