Terror group Islamic State has released a propaganda video in which an 80-year-old cleric from Xinjiang calls on Muslims in the mainland province to join IS and fight against the "Chinese infidels". The cleric, named in some reports as Muhammed Amin, claims to have once been an imam at a mosque in Xinjiang. He says he joined Islamic State in Syria after learning his son had died fighting for the group. The 21-minute tape, uploaded to the internet last month, appears to have been released from Aleppo in Syria. The video also shows a classroom full of Uygur boys dressed in headgear bearing the black-and-white IS logo. One of the boys points to the IS flag as he pledges: "O Chinese infidels … we will come to you and raise this flag in Turkestan." Turkestan is the name Uygurs give to Xinjiang. The 80-year-old cleric, who speaks in a Turkic language, does not say when he arrived in Syria but says he came with his four grandsons, daughter and wife as he longed to be in a place where Islam was practised and he could fight for the Islamic cause. The cleric, who appears to be a symbolic leader of the Uygurs in IS, says he was trained for combat. "I went to training camp, and I crawled, I ran and I rolled. I did almost everything and ended training camp well," he says. While he asked to fight, he was not allowed due to his age. The man, with a long, flowing white beard, holds a Kalashnikov rifle throughout the interview as he recalls the persecution his fellow Muslims face in Xinjiang. He says they are forced to study their religion in private and the girls are not allowed to wear their veil in public. Often, they are arrested and beaten, he says. Even as an imam, he was not allowed to practise Islam fully, he says. "My heart was filled with sorrow living under the rule of the Chinese idolaters." Chinese authorities work hard to "corrupt the hearts of our children", he says, adding that he left his mosque about 20 years ago to live in an apple orchard "far away". He says he taught students there but they were arrested. Authorities exiled him when the students described killing a Chinese, and how being killed in turn would make them martyrs. The cleric says he is happy to be living in territory controlled by Islamic State. Towards the end of the video, he refers to Xinjiang doctors helping IS. One such doctor then explains the work they are doing in Syria. The 80-year-old says: "I call on the doctors, engineers and teachers amongst our brothers in Turkestan to come and serve Islam in the land of the Islamic State." Commenting on the Uygur boys in IS, Rohan Gunaratna, a terrorism expert from the S. Rajaratnam School of International Studies, said: "This means the terrorist threat to China will persist beyond the current generation of terrorists."