Tibet, April 12 -- Global Tibet advocacy groups have voiced serious concern and are urging a full and transparent investigation into the death of Tulku Hungkar Dorje Rinpoche, a highly revered Tibetan lama who died under suspicious circumstances in the custody of Chinese authorities in Vietnam late last month.

On Friday, Tibetans in exile also held a candlelight vigil in Dharamshala (India) to mourn the death of Tibetan religious leader Rinpoche (56), who had reportedly sought refuge in Vietnam after experiencing harassment from Chinese authorities in Tibet due to his active role in preserving Tibetan language and cultural identity.

According to multiple sources, he was arrested in Ho Chi Minh City on March 25 during an operation said t...