Sea mines might have caused the tragic sinking of a South Korean naval ship, U.S. experts said Saturday, dismissing concerns over possible North Korean involvement. "I doubt that North Korea was involved in the incident," John Feffer, co-director of the Foreign Policy in Focus program at the Institute for Policy Studies, said. "It didn't seem to involve any artillery fire from the North." The 1,200-ton "Cheonan" sank Friday night (Seoul time) after a mysterious explosion that South Korean witnesses and military officials say split the vessel in two. Only 58 of the 104 crew aboard were rescued. The others are...