Human Rights Watch is accusing China of putting strong pressure on Nepal to restrict the rights of Tibetans living in that country.
The group says in a new report Tibetans face excessive use of force by Nepalese police, arbitrary arrests, spying, and threats.
Human Rights Watch (HRW) says Nepal is under huge pressure from China to limit the number of Tibetans who can enter the country, in violation of international law.
Senior HRW researcher Nicholas Bequelin says the problem has been going on for more than half a decade.
"Well our report shows that the situation of the Tibetan community in Nepal, which is approximately between 15,000 and 20,000 people, has markedly deteriorated since 2008. 2008 was the year when we saw mass protests on the Tibetan plateau in China that took Beijing by surprise to a large extent. And since then, China seems to have considered that it has to enroll Nepal's government help in surpressing the Tibetan community in Nepal itself."
Nepal has long been a refuge to Tibetans seeking to escape repression from China, and has also agreed to be a transit point for Tibetans going to India.
Nepal has not responded to the new report.
China accuses Tibetans of terrorism in fighting for an independent state. Exiled Tibetan spiritual leader the Dalai Lama says Tibetans only want more autonomy inside China.
(This report was produced in collaboration with the VOA Mandarin service.)