BBC News - North Korean leader Kim Jong-un sends envoy to China:
"Chinese media said Mr Choe met Wang Jiarui, a top foreign affairs official.
The visit - the duration of which remains unknown - follows weeks of high tension on the Korean peninsula.
China is North Korea's biggest trading partner and closest ally. It has traditionally sought to maintain stability in North Korea, avoiding any crisis that could trigger the fall of the regime and propel a flow of refugees across the border.
But in recent weeks, following Pyongyang's 12 February nuclear test and amid strident rhetoric from its leaders, China has expressed frustration with North Korea, with state media openly debating the benefits of close ties."