Free Tibet director Stephanie Brigden also said that the protesters, as young as 15, were the youngest to self-immolate and that the timing of Wednesday's protests in ethnic Tibetan areas of China appeared aimed at the party's weeklong conference to unveil the country's new leadership that opened Thursday.
The three monks set fire to themselves Wednesday afternoon outside a police office in southwest Sichuan province calling for freedom for Tibet and the return of their spiritual leader, the Dalai Lama, Free Tibet said in a statement. It said it was the first documented case of a triple self-immolation.
The youngest monk, identified as 15-year-old Dorjee, died at the scene and his companions, Samdup and Dorjee Kyab, both 16, were taken to a hospital by security forces and their conditions were unknown, Free Tibet said.
Then in the evening a 23-year-old Tibetan nomadic woman, Tamdin Tso, died after self-immolating in another ethnically Tibetan area in western Qinghai province, it said. She took petrol from a motorbike and set fire to herself in the family's winter pasture near Tongren, a monastery town, and her body was taken back to her family's home whether people gathered to pray, it said. She had a 5-year-old
Free Tibet's accounts could not immediately be confirmed.
A man at Qinghai provincial government's news office said he didn't know about the case and hung up. The Aba prefecture's communist party propaganda department referred queries to prefectural and provincial authorities, where calls rang unanswered.
Since March 2011, dozens of ethnic Tibetans have self-immolated in ethnically Tibetan areas to protest what activists say is China's heavy-handed rule over the region.
Chinese authorities routinely deny Tibetan claims of repression and have accused supporters of the Dalai Lama of encouraging the self-immolations. The Dalai Lama and representatives of the self-declared Tibetan government-in-exile in India say they oppose all violence.
Free Tibet said the three boys came from a village in Aba county, a region of high-altitude valleys grazed by yaks on the Tibetan plateau, and belonged to Ngoshul Monastery, which houses around 130 monks and is approximately 10 kilometers (6 miles) from Ngaba town where other self-immolations have taken place. Free Tibet said security forces had been deployed to the monastery and the nearby town of Gomang, and already heavy restrictions in Ngaba county had been intensified, with people unable to leave or enter Ngaba town.
"In just one day, on the eve of the Communist Party Congress, four Tibetans have set fire to themselves," Brigden said. "These protests are aimed at sending the next generation of China's unelected regime a clear signal that Tibetans will continue to fight for their freedom despite China's efforts to suppress and intimidate them."
Free Tibet says over two thirds of those who have self-immolated are younger than 25 and have grown up under Chinese rule. "Their protests belie China's propaganda that Tibetans are happy and thriving. Tibetans young and old, men and women from all walks of life across a vast area of Tibet are setting fire to themselves in protest at China's occupation," it said in a statement.
The Chinese government has poured money into the region for years to spur development and helping to raise living standards. But many Tibetans say China's tight control, including on religious observance, is draining them of their culture and identity.