BEIJING — China must immediately reveal the whereabouts of a leading Mongol dissident who has disappeared along with his family since completing a 15-year prison term last week, Amnesty International said.

Hada, who like many Mongols goes by one name, on Friday completed a sentence handed down in the 1990s on charges of espionage and "splitting the country" after he led calls for greater freedoms for China's six million ethnic Mongols.

But authorities in China's Inner Mongolia region remain mum on whether he is free, and earlier this month his fellow activist wife Xinna and their son Uiles disappeared into police custody ahead of the expected release.

"The Chinese authorities must immediately clarify Hada and his wife and son's current status and whereabouts," Catherine Baber, Amnesty International?s Asia-Pacific Deputy Director, said in a statement issued Wednesday.

"They cannot simply hide people they find embarrassing or inconvenient."

Baber said China was using "enforced disappearances" to clamp down on activists amid world attention on the plight of jailed 2010 Nobel Peace laureate Liu Xiaobo.

Liu, a dissident writer, was jailed in December 2009 on subversion charges after co-authoring a petition calling for reform of China's rigid one-party Communist political system and respect for human rights.

Pictures dated December 10 have been anonymously posted on an overseas human rights news website showing Hada and his family reunited and sharing a meal.

The US-based Southern Mongolian Human Rights Information Center (SMHRIC) quoted Xinna's sister as saying police has told family members the three were having a "happy family reunion in a five-star luxury hotel".

However, there has been no word on when or if Hada and his family would be allowed to return home to Hohhot, capital of the Inner Mongolia region, which lies in northern China and borders Mongolia.

Many of China's ethnic Mongols, who have cultural and ethnic ties with Mongolia, complain of political and cultural repression by China. Some refer to Inner Mongolia as "Southern Mongolia".

One of China's longest-jailed prisoners of conscience, Hada fell foul of authorities through writings in which he called for Mongol autonomy, and after organising peaceful demonstrations as head of the underground Southern Mongolian Democracy Alliance.