BEIJING, China - A relative of a Mongolian activist set to be released Thursday from a Chinese prison said the man's wife and son are now in police detention and he himself has been warned to keep silent.

The scheduled release of Hada, who like many ethnic Mongolians uses just one name, has brought a round of complaints about police harassment.

While separatism among Mongolians living in Chinese-controlled Inner Mongolia is not well known, it's a hot-button issue for the government, which fears the spread of the violent ethnic unrest that has hit Tibet and Xinjiang in recent years.

Hada, 56, helped found the Southern Mongolian Democratic Alliance seeking to establish an independent nation in Inner Mongolia. He was sentenced to 15 years in prison a year later after being accused of separatism and spying.

The uncle of Hada's wife said by telephone Thursday that police have detained Hada's wife and son, and there was no word on the activist's scheduled release.

"Last week the police came to visit me twice, once at home and once at my workplace. They said it would be better if I didn't pick up telephone calls from outside," Mascholu said. "Definitely I'm being watched. The police told me to be careful."

The main telephone numbers for the No. 4 prison in Chifeng city, where Hada served his prison sentence, and the Inner Mongolia Regional Detention Center in Hohhot city rang unanswered Thursday.

Hada's son, 28-year-old Wei Lesi, told The Associated Press on Saturday that police had raided the family bookstore and taken away his mother, Xinna.

Shortly after that, police took away Wei Lesi, Mascholu said.

Cell phones belonging to Wei Lesi and Xinna were turned off Thursday.

The U.S.-based Southern Mongolian Human Rights Information Center said several Mongolian dissidents in China have been unreachable recently, including the writer Govruud Huuchinhuu, who was detained last month and put under house arrest for trying to organize a rally to welcome Hada's release.