A spy plane crashed Friday during routine training and its two pilots were presumed dead in the second military accident to strike South Korea while it hosted the Group of 20 summit of major economies, an air force official said. South Korea was on heightened alert for possible provocation by communist neighbor North Korea during the two-day G-20 summit, but there was no indication of the North's involvement in either the plane accident or the sinking Thursday of a 150-ton naval vessel.The RF-4C patrol aircraft hit a mountain in Jeonju, 130 miles (210 kilometers) south of Seoul, around 12:30 p.m. (0330 GMT), about 40 minutes after taking off from a base in Suwon, just south of Seoul, the official said. He spoke on condition of anonymity, citing internal policy.Two bodies believed to be the pilots were found at the mountain, said the official, adding that no civilian was hurt on the ground. The air force launched an investigation to determine the cause of the crash, and it would take time to reach a final conclusion, he said.South Korea operates about 20 secondhand U.S.-made RF-4C spy planes after purchasing them from the U.S. air force, according to South Korea's air force. The crash came just a day after a South Korean navy ship sank after colliding with a larger fishing boat in waters northwest of the southern resort island of Jeju.The G-20 summit which was wrapping up Friday in Seoul has put a spotlight on security, because North Korea has a history of acting provocatively when world attention is focused on South Korea.The Korean peninsula officially remains in a state of war because the 1950-53 Korean War ended in an armistice, not a peace treaty.