Experts investigating the blast which sank a South Korean warship are checking salvaged metal fragments against a North Korean torpedo which Seoul retrieved seven years ago, a report said Thursday. South Korea has mounted a multinational probe into what caused the explosion which split the 1,200-tonne corvette the Cheonan in two near the disputed border with the North on March 26. "Comparisons are underway to check if metal pieces recovered from the Cheonan are made of material similar to that of a North Korean torpedo," an unidentified military official told Yonhap news agency. The official was quoted as saying the...