South Korea is staging one of its largest ever military drills amidst tense relations with the North. Hundreds of troops, tanks, helicopters and jet fighters are gathering some 20 kilometers from the heavily armed land border. Tension has been high since North Korea shelled the South's Yeonpyeong island last month, killing four South Koreans. The North has branded the exercises war mongering but its criticism has been more muted than normal. Today's drill is being held at Pocheon, about 50 kilometers from central Seoul.