Hada was tried in China's vast northern Inner Mongolia region in 1996 and sentenced to 15 years in jail for separatism and spying and supporting the Southern Mongolian Democratic Alliance, which sought greater rights for ethnic Mongolians.

But after completing his jail sentence, he had to serve a separate sentence, Tao Jian, the deputy Communist Party boss of Inner Mongolia's law and order committee, said on the sidelines of China's on-going meeting of parliament.

"He was released in December 2010. But is he still serving out his four years of deprivation of political rights," Tao said, in the first public remarks on the case in years.

"During this time, in accordance with the law, certain of his activities have been limited. But Hada is in a safe, healthy and guaranteed environment. That's all I have to say."

Chinese authorities often place released political prisoners under house arrest or otherwise restrict their movements and contact with the outside world. Officials, though, rarely give details of individual cases.

Hada's wife Xinna, who has denied her husband was a separatist, and son Uiles were detained in the run-up to his release and rights groups believe they are also still being held. Many Chinese Mongolians go by only one name.

Tao would not comment on Xinna's fate, nor say where her and her husband were being held.

Ethnic Mongolians, who make up less than 20 percent of the roughly 24 million population of Inner Mongolia, have long complained that traditional grazing lands have been ruined by mining and desertification, and that the government has marginalized their culture and language.

Inner Mongolia was rocked by protests in May last year over the death of an ethnic Mongolian herder who was hit by a truck after taking part in protests against pollution caused by a coal mine.

(Reporting by Ben Blanchard; Editing by Ed Lane)