The sometimes violent demonstrations — which prompted a swift and sustained crackdown by security forces — was the largest Tibetan protest against Chinese rule since the failed March 10, 1959 uprising against communist authorities who fought their way into the Himalayan region in 1950.
The upcoming anniversaries have prompted authorities — who are wary of unrest during this sensitive period — to declare Tibetan areas off-limits to foreigners and to reportedly crack down violently on demonstrators.
The Tibetan Center for Human Rights and Democracy said the two nuns were among a group of 55 detained after a peaceful protest on May 14 outside government offices in Garze, a prefecture in Sichuan province.
The center identified them as Soe Lhatso, 35, who was sentenced to 10 years in prison, and 36-year-old Bhumo, who was sentenced to nine years. Both were nuns at the local Pangri Na Buddhist convent, it said.
The center did not say what they had been charged with or give an exact date for when the sentences were handed down.
Separately, the center said two 18-year-olds, Ngawang Tashi and Dorjee Tashi, were sentenced to three years each for joining in a protest in Garze on March 18 last year. No details were given.
A clerk at the Garze court said all cases related to last year's demonstrations had been resolved but refused to answer questions about the two most recently reported, and hung up.
State media says 76 people have been sentenced and more than 950 detained following last year's protests. Beijing says 22 people died, but Tibetan supporters say many times that number were killed in the protests and subsequent military crackdown.
Tensions appeared to be running high in China's Tibetan-inhabited regions ahead of the two critical anniversaries. Seeking to head off unrest, a Communist Party official in Tibet warned Buddhist clergy this week against political activity and ordered them to denounce the 73-year-old Dalai Lama, Tibet's spiritual leader who fled into exile in India amid the 1959 uprising.
Tibetan advocacy groups reported two separate incidents of anti-government or anti-Chinese unrest this week alone. One, in the Sichuan province town of Lithang, led to an attack by paramilitary troops on protesters Monday in which several were injured and at least 21 detained, according to two Tibet advocacy groups.
In the other, reported by the Washington-based International Campaign for Tibet, troops opened fire Thursday on a crowd of Tibetans that had overturned and burned police cars while shouting anti-Chinese and pro-Dalai Lama slogans in the Tibetan town of Nagchu. It wasn't clear if there were casualties.
Phone calls to Nagchu police headquarters were cut off without being answered. A man in the local Communist Party propaganda office said he knew nothing about any incident and hung up. Authorities in Lithang refused to comment.
Given the regime's secretive nature, individual incidents are difficult to confirm independently.
China claims that Tibet has been a part of its territory for four centuries, while many Tibetans say they were effectively an independent state for much of that time.