North Korea warned Saturday that South Korea will face a \"catastrophic situation\" if it allows anti-Pyongyang propaganda leaflets to be flown into its territory across the border ahead of a major holiday.A group of North Korean defectors and a Seoul-based civic organization have said they jointly plan to fly tens of thousands of leaflets with anti-Pyongyang messages, often mixed with U.S. dollar bills, via balloon timed to the upcoming birthday of the North\'s late founder Kim Il-sung, which falls on Monday.