U.S. based Human Rights Watch is asking China to account for at least 17 ethnic Uighurs forcibly returned from Malaysia, Thailand and Pakistan in August.
The rights group also said China should stop pressuring countries to deport ethnic Uighurs.
An HRW official says China should honor the rights of individuals seeking asylum.
HRW Refugee Director Bill Felick says China should immediately allow international organizations access to Uighurs already returned.
The Uighurs are a Turkic-speaking, mainly Muslim ethnic group living in far western China. Beijing accuses some Uighurs of involvement in Islamist terrorism.
Chinese officials have also blamed Uighur groups for several violent uprisings in the Xinjiang region.
Uighurs and Han Chinese clashed in ethnic rioting in 2009, resulting in the deaths of 197 people.
Some information for this report was provided by AP, AFP and Reuters.