The two Koreas briefly exchanged naval fire today along their disputed western sea border, with a North Korean ship suffering heavy damage before retreating. South Korean military Joint Chiefs of Staff said in a statement that there were no South Korean casualties. It is not immediately clear if there were any casualties on the North Korean side. Each side blamed the other for violating the sea border. The clash the first of its in kind in seven years occurred as US officials said President Barack Obama has decided to send a special envoy to Pyongyang for rare direct talks on the communist country's nuclear weapons programme. No date has been set but it would be the first one-on-one talks since Obama took office in January. Obama is due in Seoul next week. North Korea's military issued a statement blaming South Korea for the grave armed provocation, saying its ships crossed into North Korean territory.