By Hyonhee Shin, Josh Smith and David Brunnstrom SEOUL (Reuters) -North Korea fired a short-range ballistic missile into the sea off its east coast on Friday, South Korea’s military said, the latest in a series of launches by the nuclear-armed country amid heightened tensions. South Korea also scrambled fighter jets when a group of about 10 North Korean military aircraft flew close to their heavily fortified border, and North Korea fired some 170 rounds of artillery into “sea buffer zones” off its east and west coasts, the South’s Joint Chiefs of Staff (JCS) said. South Korea’s National Securi…