An international report has found that a North Korean submarine's torpedo sank a South Korean Navy ship on 26 March causing the loss of 46 sailors. Investigators said they had discovered part of the torpedo on the sea floor and it carried lettering that matched a North Korean design. However, Pyongyang rejected the claim as a fabrication, South Korea's Yonhap agency reported. It said the North threatened war if sanctions were imposed by the South. But, South Korean President Lee Myung-bak has pledged to take stern action against the North for its alleged attack on a South Korean warship. South Korea's Yonhap News Agency reported that a joint investigation committee today announced in Seoul that they had concluded a North Korean submarine fired a torpedo that sank the South Korea warship in March. The committee comprised of American, Australian, British and Swedish, as well as South Korean, experts. <br/> The White House called the report objective and scientific. The United States described the sinking of the ship as an act of aggression by North Korea that challenged peace. UN Secretary General Ban Ki-moon said the report was deeply troubling. The Cheonan went down near the disputed inter-Korean maritime border, raising tension between the two nations, which technically remain at war. The shattered wreck of the 1,200-tonne gunboat was later winched to the surface, in two pieces, for examination.<br/>