SEOUL, Nov 13, 2009 (AFP) - North Korea vowed Friday to take "merciless" military action to protect its Yellow Sea border with South Korea and warned that Seoul would pay dearly for a naval clash this week.
"Our side reminds your side again that there exists only a demarcation line in the West Sea (Yellow Sea) set by our side, and from this moment on we will take merciless military measures to protect it," its military said in a message to the South's forces.
The North refuses to recognise the sea borderline set by the United Nations after the 1950-53 war and demands that it be drawn further to the south.
The new warning came just five days before US President Barack Obama visits Seoul for talks expected to focus on North Korea's nuclear programme.
The letter, quoted by Pyongyang's Korean Central News Agency, renewed demands for an apology for Tuesday's clash, in which Seoul says a North Korean patrol boat was badly damaged. It called for punishment for those responsible.
"The South side will be held responsible for acts aimed at destroying national reconciliation and unity and hampering peace and unification, and it will have to pay dearly," it said.
Seoul says the North's boat crossed the border, ignored five warnings to turn back and then opened direct fire at a South Korean boat. It said South Korean boats returned fire and set the intruder ablaze.