North and South Korean warships have exchanged fire along the world’s last Cold War maritime border. No-one was reported hurt in the incident, but it is thought vessels from each side were damaged.The skirmish happened in the Yellow Sea along what is called the Northern Limit Line. South Korea claims it was triggered by Northern vessels venturing into Southern waters around 10.30am local time, which prompted a two-minute shoot-out. General Lee Ki-Sik at South Korea’s Joint Chiefs of Staff said: “We fired warning shots, and the North Korean patrol ship fired directly at us. Then we fired back. None of our troops were injured” The timing of this incident may be significant. President Obama is due to visit Asia later this week, and North Korea has a habit of flexing its military muscles ahead of major regional events. Pyongyang is seeking direct talks with America over its nuclear programme, and last week boasted of producing more weapons-grade plutonium.