Free Tibet, a rights group in London, said the self-immolations -- the latest in a series of such acts by protesting Tibetans --- occurred Wednesday. One of the three boys died, while the other two were believed to have survived.
The incident came a day ahead of the start of the weeklong Chinese Communist Party's 18th Congress in Beijing called, among other things, to announce the once-in-a-decade change of leadership.
"The three young monks aged 15 and 16 mark what is the first triple self-immolation protest to happen in Tibet. One died and the other two are thought to have survived," Free Tibet said on its website.
"The young boys called for freedom in Tibet and for the return of the Dalai Lama. Immediately after their protests, Chinese security forces arrived at the scene and cordoned off the area."
The report said the youngest of three, identified as 15-year-old Dorjee, died at the scene. The other two, both 16, were taken to hospital by Chinese security forces and that their "current whereabouts and wellbeing are unknown."
All three belonged to the Ngoshul Monastery, close to Ngaba County in China's Tibetan areas where many other self-immolation protests have occurred, the announcement said.
"Intensified security measures have already been enforced throughout Ngaba County where Tibetans are unable to leave or enter the area," the announcement said.
At least 58 Tibetans have set themselves on fire since the latest round of protests against Chinese rule of their homeland began in February 2009.
The Dalai Lama, the spiritual leader of the Tibetans who lives in exile in Dharamshala, India, has been accused by China of instigating the protests. The Buddhist leader and the Tibetan government-in-exile in India have said they oppose all forms of violence.
In his keynote address at the opening of the party congress Thursday, outgoing Chinese President Hu Jintao said that after 90 years of hard struggle, the Communist Party, which has ruled the country since 1949, has led the people of all ethnic groups in the country into an increasingly prosperous and powerful new China.
Despite such claims, China faces major challenges such as the Tibetan protests and the violent ethnic tensions in its northwest Xinjiang-Uighur region where the Turkic-speaking minority Muslim Uighurs resent being ruled by the majority Han Chinese.