Chinese authorities said a Tibetan woman who died after setting herself on fire in northwestern China on Saturday had suffered a head injury before the incident, state media reported. Overseas rights groups say three Tibetans, including the woman in Gansu province, have self-immolated in China in recent days as Beijing tightens security ahead of the sensitive anniversary of deadly 2008 riots. Tsering Kyi, reported to be aged between 16 and 20, set herself alight on Saturday at a vegetable market in Maqu county, Xinhua said late Tuesday, confirming earlier reports by activist groups. Xinhua said the woman was a school student and had suffered "occasional fainting spells" after hitting her head on a radiator in a classroom and falling into a coma. "The medical treatment held up her studies and her school scores began to decline, which put a lot of pressure on her and made her lose her courage for life and study," Xinhua said, citing local police. The Xinhua report did not say when the accident happened nor did it mention the other two self-immolations that occurred on Sunday and Monday. An 18-year-old man self-immolated on Monday in restive Aba prefecture in the southwestern province of Sichuan, a day after a mother of four died after setting herself alight in the same region, according to London-based Free Tibet and International Campaign for Tibet. These same rights groups say more than 20 people have set themselves on fire in Tibetan-inhabited areas of China over the past year, mostly in Sichuan, in protest at what they see as repressive Chinese rule. China has substantially increased security in its Tibetan-inhabited areas since the deadly riots which began in the Tibet region's capital, Lhasa, in March 2008 before spreading to other areas. Beijing accuses the Dalai Lama, Tibet's spiritual leader, of inciting the self-immolations in a bid to split Tibet from the rest of the nation. Li Changping, a senior communist official in Sichuan, said Wednesday the series of self-immolations would not disrupt the stable development of Tibetan-inhabited regions, Xinhua reported. Li, speaking at the country's annual parliamentary meeting in Beijing, blamed the unrest on the Dalai Lama and his supporters and said their activities were "doomed to fail".