Chinese President Xi Jinping will visit North Korea next week, state media said Friday, the latest in a series of high-level summits as Beijing asserts its position as a diplomatic superpower on the world stage.State broadcaster CCTV said that Xi would visit from June 8 to 9 at the invitation of North Korean leader Kim Jong Un, his first trip to Pyongyang in seven years.Beijing is a vital source of political and economic support to North Korea, which is one of the most diplomatically isolated countries in the world and under heavy international sanctions.