At least 15 Falun Gong practitioners have died in custody since the group was banned nine months ago, the Hong Hong-based Information Center for Human Rights and Democracy said.
The government has disputed some of those claims, saying practitioners committed suicide or died of natural causes, not because of any mistreatment.
The Information Center cited family members of those killed, unidentified officials and unidentified Falun Gong practitioners.
It said Zhang Zhenggang, a 36-year-old bank worker and Falun Gong organizer in Huaian city in eastern Jiangsu province, was beaten March 25 by a guard and another prisoner with wooden batons, leaving him in a coma.
Five days later, police took the comatose Zhang, who was still breathing and had a pulse, from the hospital to a crematorium, the Information Center said.
``Zhang Zhenggang may still have been alive when he was cremated,'' it said.
A city police official, contacted by telephone, said he knew nothing about the case.
The Information Center said Falun Gong member Guan Chaosheng was beaten to death by police in Beijing after he came to the capital to protest.
Members have been coming to Beijing almost every day to protest the ban, and are often picked up on Tiananmen Square.
The Information Center said authorities paid $1,200 in compensation to Guan's family.
A police official in Guan's hometown, in Qidong county in southern Hunan province, said he did not know about the case.
Falun Gong member Li Yanhua died April 14 in a labor camp after a hunger strike, the Information Center said.
Li, an employee at an aircraft manufacturer in Nanchang, a city in the southern province of Jiangxi, was sentenced in January to two years in prison after she came to Beijing to protest, the group said.
It said 60 other Falun Gong members imprisoned in the labor camp are on a hunger strike that began April 4.