South Korea''s navy rescued three North Korean fishing boats and seven fishermen near the yellow sea border between the Koreas, a defense ministry spokesman said on Friday. South Korea also refueled a North Korean fishing boat that drifted into its waters and returned it back North, the South spokesman said. The four North Koreans who were adrift on the two boats were discovered two hours apart Thursday night. South Korean intelligence officials are investigating to determine whether they intentionally defected. This incident is a departure from recent tensions between the two Koreas along the maritime border. On Wednesday, South Korea fired back at North Korea after it said three shots from the North hit waters close to the maritime border.