Kalsang Yarphel, 39, a popular Tibetan singer arrested last year for singing political anti-Chinese songs, has been sentenced to four years in prison by a court in Chengdu, the capital of Sichuan province. His producer Pema Rinzin and two other associates were also sentenced. UK-based Free Tibet has launched a petition urging China to free all Tibetan performers in custody which has won support from musicians in the West.