North Korea threatened on Friday to open fire on South Korea if it allows activists to go ahead with plans to drop anti-North leaflets on its territory, its most strident warning against its long-time foe in months.North Korea, which is still technically at war with the South after their 1950-53 conflict ended in merely a truce, often uses shrill rhetoric denouncing its rich, capitalist neighbour and threatening all-out war.A looming presidential election in the South and plans to deploy longer-range missiles by the government in Seoul have angered the North and prompted an escalation of belligerent commentaries from Pyongyang."We had similar threats last year and they did not stop us before and this is not going to stop us this time,” said Pak Sang-hak, a North Korean exile who defected to the South 12 years ago.He is the leader of a coalition of groups of North Korean exiles and human rights activists who plan to launch giant balloons containing 200,000 leaflets criticising North Korea’s government for the second year running.Some of the leaflets, printed on plastic bags, will contain $1 bills. As well as the dollars, the bags themselves are said to be prized by North Koreans, many of whom often lack daily necessities.South Korea’s defence minister told parliament that its military would retaliate in the event of any attack.South Korea’s military has come under pressure after it failed to detect a North Korean soldier walking across the world’s most heavily armed border until he knocked on the doors of soldiers’ barracks.