Seoul - South Korea on Wednesday accused rival North Korea of floating propaganda leaflets down a river in the first such incident.South Korea's military discovered dozens of plastic bags, each carrying about 20 leaflets, near the estuary of Seoul's Han River close to the tense Korean border last Friday, according to the South's Defence Ministry. Seoul is only an hour's drive from the border.The leaflets contained threats to launch missile attacks and a repeat of the North's long-running propaganda such as that the North won the 1950-53 Korean War, a ministry official said, requesting anonymity because of department rules.The war ended with no one's victory. An armistice that stopped the fighting has yet to be replaced with a peace treaty, leaving the Korean Peninsula split along the world's most heavily fortified border and at a technical state of war. Wednesday marks the 63rd anniversary of the armistice's signing.North Korean recently warned of unspecified "physical" measures in response to a US plan to deploy an advanced missile defence system in South Korea by the end of next year. North Korea last week fired three ballistic missiles into the sea, according to Seoul defence officials.The rival Koreas resumed old-fashioned, Cold War-era psychological warfare in the wake of North Korea's fourth nuclear test in January.Seoul began blasting anti-Pyongyang propaganda broadcasts and K-pop songs from border loudspeakers in retaliation for the North's atomic detonation. Pyongyang quickly matched Seoul's campaign with its own border broadcasts and launches of balloons carrying anti-South leaflets across the border.The latest discovery of propaganda leaflets marks the first time for North Korea to use a river to send leaflets, according to the South Korean defence official. He said North Korea is believed to have used a river because the direction of the wind isn't favourable in the summer to fly propaganda balloons from north to south.Many in South Korea believe their broadcasts could sting in Pyongyang because the rigidly controlled, authoritarian country worries that the broadcasts will demoralise front-line troops and residents and eventually weaken the grip of absolute leader Kim Jong Un.Nearly 30 000 North Koreans have fled to South Korea since the end of the Korean War, mostly for political and economic reasons. South Koreans defecting to the impoverished, authoritarian North is highly unusual.