Police have taken into custody the wife and son of China's most prominent ethnic Mongol dissident, a rights group said Wednesday, just days before the jailed activist is due to be freed from prison.

Hada will complete a 15-year jail term on Friday for espionage and separatism charges after he advocated greater freedoms for China's six million ethnic Mongols.

His wife Xinna and their son Uiles were taken away by police in Hohhot, capital of China's Inner Mongolia region, on Saturday, the U.S.-based Southern Mongolian Human Rights Information Center (SMHRIC) said in a statement.

The bookstore run by Xinna in the city, which has long been a symbol of Mongol dissent, also has been shut down, it said.

Xinna, 54, told AFP last month that prison authorities were preventing her from visiting Hada, 55, and were harassing his supporters, apparently fearful that his release could draw attention to Mongol discontent.

“There are many people wanting to see him and whom he will want to see after such a long time,” she said, adding that Hada would likely resume his advocacy work after regaining his health.

She said he suffered from a range of illnesses worsened by prison conditions and being deprived of proper medical care.

Phone calls to Xinna's bookstore and cell phone went unanswered, as did calls to Hohhot police and the detention centre where she and Uiles were said to be held.

Many Mongols, who have more of a cultural and ethnic affinity with the republic of Mongolia to the north, complain of political and cultural repression by China.

The Mongol rights group said ethnic Mongolian dissidents and activists who peacefully exercise their constitutional right to free speech and assert their human rights “are at constant risk of arrest and imprisonment.”

It called on the international community to exert pressure on Beijing to “end its ongoing arbitrary detention of Mongolian dissidents and activists, elimination of Mongolian culture, language and identity and destruction of the natural environment in Southern Mongolia.”

One of China's longest-jailed prisoners of conscience, Hada fell foul of China's government in the 1990s after organizing peaceful demonstrations for Mongol rights as head of the underground Southern Mongolian Democracy Alliance.