South Korea bans propaganda balloons after strike threat from the North Pyongyang has repeatedly protested at similar incursions in the past, but the vehemence of its latest threats apparently convinced authorities in the South to close the area around Imjingak, on the edge of the Demilitarised Zone, to defectors from the North, their supporters, local residents and journalists. Members of the Fighters for Free North Korea had planned to send 200,000 leaflets attached to balloons over the border from 11 am, but South Korean troops and police banned access to the site. A warning carried by North Korea state media described the plan as "an unpardonable challenge to the army and people of the DPRK and a deliberate act to push north-south ties to the lowest ebb." Accusing the South Korean government of being behind the plan and of carrying out psychological warfare in an attempt to topple the regime, it said the Korean People's Army would make the launch sites "targets of direct firing" and demanded that residents evacuate the area. Pyongyang is also likely to have been angered by the visit by Lee Myung-bak, the South Korean president, to the island of Yeonpyeong on Thursday. The island, close to the disputed sea border between the two nations, was shelled in November 2010 by North Korean artillery, killing four people and injuring 19. In response, the South raised its military alert levels and deployed artillery and tank brigades. Combat air patrols have also been stepped up. "If (the North) launches attacks, (the South Korean) military will strongly and thoroughly retaliate against the origin of the attacks and their supporting forces under the right of self-defense," Kim Min-seok, a spokesman for the defence ministry, told Yonhap news. We are closely watching the North Korean military's movements. A police official said the ban on people entering the area was due to "safety concerns over North Korean warnings, clashes between anti- and pro-civic groups and complaints from residents."