Two former monks at the Kirti monastery, set themselves on fire in Sichuan province to protest China's occupation of Tibet. One of the former monks, a 19-year-old, was declared dead at the scene, Tibetan activist agency Free Tibet said.
The group said there have been seven self-immolations in the region since March.
Victoria Nuland, a spokeswoman for the U.S. State Department said Washington was "very concerned about this trend."
She said Washington has "repeatedly" called on Beijing to respect the rights of Tibetans to express themselves and to do more to address regional tensions.
Human Rights Watch called on Beijing to end "excessive restrictions" in the area and lift "heavy-handed security measures imposed on other lay communities and monasteries in the region."
The rights group said it had documented reports of violent security raids, arbitrary detentions of Tibetan monks and constant surveillance of religious activity in the region.
"Security measures designed to curtail the right to free expression, association, and religious belief in Tibetan monasteries are not legitimate," Sophie Richardson, China director at Human Rights Watch, said in a statement.