North Korea warned Friday that it would mercilessly defend itself in disputed waters where a bloody naval clash with rival South Korea took place this week, further raising tensions ahead of a visit to Seoul by US President Barack Obama. The North's military issued the warning in a message sent to South Korea, according to Pyongyang's official Korean Central News Agency. The message was sent by a high-ranking officer who heads the North Korean military delegation that occasionally holds talks with South Korea's military. Two state newspapers issued a similar warning Thursday, though analysts played down the threat as they were not issued by the military itself. The military also repeated a demand that South Korea apologize over the clash off their western coast Tuesday that a senior South Korean military officer said left one North Korean officer dead and three others wounded. North Korea also reiterated it would not honor the Northern Limit Line, a de facto western sea border drawn up by the UN command at the end of the 1950-53 Korean War. The divided Koreas have long been at odds over the western sea border. The North has insisted the line be redrawn farther south, a demand rejected by South Korea. North Korea's military said it "will take merciless military measures to defend" its interpretation of the border "from this moment." South Korea's defense ministry said its position on the sea border remains unchanged. The Joint Chiefs of Staff had no comment. The North's military also said the South will be forced to pay a heavy price over what it claims was South Korea's intentional provocation. The two sides have accused the other of provoking the two-minute battle on Tuesday. South Korea suffered no casualties. The two Koreas have remained technically at war since the Korean War ended with an armistice, not a peace treaty. The US, which has never had diplomatic relations with North Korea, stations 28,500 troops in South Korea to deter potential North Korean aggression. Obama is due to arrive in Seoul Wednesday as part of a regional trip. In related news, French Pyongyang envoy Jack Lang stated on Friday that talks with North Korean officials during his five-day visit to the city were "intense, frank and cordial." Lang, a former French culture minister recently appointed as Sarkozy's special envoy to North Korea, said he is on a mission to explore possible diplomatic ties between France and the communist country. France and Estonia are the only European nations that do not have formal relations with Pyongyang. Lang told broadcaster APTN in Pyongyang he was able to speak "freely" to North Korean officials, including No. 2 leader Kim Yong Nam and Foreign Minister Pak Ui Chun, on a wide range of issues. He described the discussions as "intense," but did not elaborate on the outcome of the talks. "We were trying to collect accurate information and make fair assessments," Lang said, adding he would update Sarkozy on the trip next week. The US president, meanwhile, embarked on a tour of Asia that will take him to Seoul, South Korea, next week following stops in Japan, China and Singapore. He arrived in Japan on Friday. Obama, in an interview with South Korea's Yonhap news agency published Friday, called North Korea a danger, but also said the country has the opportunity to improve its standing in the international community if it gives up its nuclear weapons. "North Korea's attempt to acquire weapons of mass destruction and the means to deliver them is destabilizing and represents a threat to peace and security," Obama said in a written response to questions from Yonhap. "By taking irreversible steps towards the complete elimination of its nuclear program, North Korea will be following the peaceful path towards security and respect," he said.