( 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 can not 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 . Just last Thursday , North Korea threatened to launch a `` sacred war '' after South Korea completed large military exercises near the volatile inter-Korean border . `` 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 .
President Lee Myung-bak tells South Koreans `` we need to stand together '' and I think that is the right thing for us as a country to do.'' Lee says : `` Our lives and the survival of the nation '' depend on national unity .