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 560 rounds of artillery into "sea buffer zones" on multiple occasions, the South's Joint Chiefs of Staff (JCS) said.Register now for FREE unlimited access to Reuters.comSeoul imposed its first unilateral sanctions against Pyongyang in nearly five years, blacklisting 15 North Korean individuals and 16 institutions involved in missile development.The incidents came after North Korea's state news agency KCNA said leader Kim Jong Un oversaw the launch of two long-range strategic cruise missiles on Wednesday to confirm the reliability of nuclear-capable weapons deployed to military units.The 16 entities blacklisted include rocket industry and naval transport agencies, as well as trading, construction and electronic firms.They aided the North's weapons programmes and helped evade international sanctions by conducting research or supplying finance and materials through overseas workers, smuggling and ship operations, the ministries said."