(CNN) -- In the face of North Korean threats, South Korean President Lee Myung-bak stepped up his nationalist push, urging countrymen in a radio address "to stand together, united as one."
"There can be no difference between you and me when it comes to national security, because our lives and the survival of the nation depend on it," Lee said Monday.
The remarks marked the latest in the war of words between the communist North and free-enterprise South, which split after Japan's defeat in World War II. Over the past six decades, small-scale skirmishes have flared repeatedly along land and sea borders, including deadly naval clashes along the demarcation line in 1999, 2002 and 2009.
The situation, if anything, has worsened in recent months -- stirred by the sinking of a South Korean warship and deadly shelling of a border island. While there previously had been movement toward reconciliation, recent events have sparked demonstrations calling for Seoul to be bolder and more defiant.
Lee referenced such attacks as "provocations against us without the slightest hesitation" in his Sunday address, saying they proved that, "if we merely let the North have its own way, national security and peace cannot be guaranteed."
The president said that Seoul had "thus far shown patience, time and again (as it) struggled to maintain peace."
Even so, he said that now was the time for South Koreans to rally as one -- and not to back down in the face of Pyongyang's threats or actions.
"If we show the North Koreans how steadfastly united we are, they will not dare challenge us," said Lee.
"The revolutionary armed forces of the (Democratic People's Republic of Korea) are getting fully prepared to launch a sacred war of justice of Korean style based on the nuclear deterrent at anytime necessary," North Korean Defense Minister Kim Yong Chun said, according to the state-run KCNA news agency.
"The South Korean puppet forces perpetrated such grave military provocation as renewing their shelling against the DPRK during their recent exercises for a war of aggression in the West Sea of Korea," Kim said. "This indicates that the enemy's scenario for aggression aimed at the start of another Korean War, has reached the phase of its implementation."
The long-planned South Korean exercises, billed as the largest land and air winter drills, were conducted in Pocheon just 15 miles from the North Korean border. More than 800 military personnel, fighter jets and anti-tank missiles took part in the exercise, which also involved more than 100 types of weapons.
Tensions have been running high since the sinking of the South Korean warship Cheonan last March, killing 46 sailors.
South Korea and the international community blamed the North for the Cheonan incident, but Pyongyang denied the accusations.
Then, last month, North Korea said the South's navy fired into Northern waters and in retaliation, it shelled Yeonpyeong Island, killing four South Koreans.
South Korea said its Navy was simply holding drills and conducted similar naval exercises again on Monday, drawing threats from Pyongyang that it would attack again. But that did not happen.