One of the 21 North Korean refugees who fled to South Korea in a small boat had brought his dog with him in an unprecedented case of canine defection, a report said Monday. The dog and the human refugees were found aboard a five-tonne boat off a South Korean island near the disputed Yellow Sea border on October 30, Yonhap news agency said. The refugees, who all expressed their desire to live in South Korea, are under interrogation at a safe house in the western port of Incheon, it said. \"The dog surprised me,\" an unnamed government official told Yonhap, adding a probe was under way over why it was brought here. The owner of the dog -- a mongrel -- was from Sonchon on the North\'s northwest coast, Yonhap said, adding refugees had never previously before brought pets like dogs. Some 21,000 North Koreans have fled to the South since the end of the 1950-1953 war, the vast majority in recent years through China. Only about 450 of the total arrived in the South by sea but the latest case was the fourth this year. In February, a boatload of 31 North Koreans arrived in South Korea, sparking weeks of acrimony. That boat drifted across the Yellow Sea border in thick fog, possibly unintentionally. Seoul returned 27 of the 31 but refused to hand over the other four despite Pyongyang\'s protests, saying they had freely chosen to stay in the South. Nine North Korean refugees were picked up by Japan\'s coastguard in September and arrived in South Korea last month. Two North Koreans were admitted to the South last month after they were found adrift in a small boat.