FACTBOX - Ties binding China and North Korea

SEOUL (Reuters) - Chinese Premier Wen Jiabao visits South Korea from Friday for bilateral talks and a regional summit sure to focus on escalating tension over North Korea, which Seoul says sank its warship, the Cheonan, in March.

China is North Korea's sole major economic and diplomatic supporter and Wen faces calls from South Korea, Japan and the United States for firmer pressure on Pyongyang over the sinking. Here is an overview of Chinese-North Korean ties.