Mongolian human rights activist Jaranbayar Soyolt hasn't been seen or heard from for almost five months – we are deeply worried that he's at risk of being tortured or ill-treated.

Jaranbayar Soyolt, who is a founding member of several exiled dissident groups in Mongolia, has been detained by Chinese authorities for alleged involvement in "overseas activities harmful to China's security". He was last seen by two business colleagues at Beijing Capital International on 6 January this year.

The 48-year-old, who was at the customs counter, handcuffed and surrounded by five policemen, told his colleagues he had been arrested. He asked them to contact his family and Beijing's Mongolian Embassy.

Passport problems

Five days later, under pressure from authorities, he phoned a colleague and said he was being held because of problems with his passport. He hasn't been heard from since.

During that phone call he asked that foreign media weren't told about this arrest in order not to "make things worse" – and because of that threat his family has not publicised his case until now.

Jaranbayar Soyolt was originally a Chinese citizen from the Inner Mongolian Autonomous Region, but he went into exile in Mongolia in the early 1990s. He was granted asylum and Mongolian citizenship in 1997.

Cultural genocide

He has been a human rights advocate for decades. In the early 1980s he was one of the leaders of the Mongolian Student Movement, a mass protest by ethnic Mongolian students and academics against the Chinese Central Government's plan to migrate 600,000 ethnic Han-Chinese into Inner Mongolia without consulting local communities.

Since living in Mongolia he has continued his human rights activities – and in 1993, he gave a speech at the World Mongolian Alliance First Congress publicly criticising China's ethnic policy as one of "ethnic cleansing and cultural genocide".

Labelled a separatist

The Chinese authorities have labelled Jaranbayar Soyolt a Mongolian separatist and have claimed that he is plotting to overthrow China's ruling communist party.

The Chinese authorities, according to their latest statement, have placed him under 'house arrest'. After originally denying any knowledge, officials confirmed on 31 January that he had entered China through the airport on 6 January.

Jaranbayar Soyolt suffers from ill-health and because of this, and the constant reports coming through of the torture and ill-treatment of political dissidents, we are extremely concerned about his well-being and safety.