Who are the Uyghurs and why are they being persecuted?

China has been accused of the mistreatment of the Uyghur people in the north-western region of Xinjiang for a number of years. This Muslim ethnic group are distinct with different culture, language and history to China's ethnic majority, Han Chinese. But why did the government start this crackdown? And what is really going on? Senior correspondent John Sudworth was based in China for nine years, and reported on the treatment of the Uyghur people. He speaks to Claire Graham to help us understand the region and how Xinjiang became a surveillance state.