In a statement issued today, Human Rights Watch noted that Zainabiddinov has been held in detention for eight months and is believed to have gone on trial two weeks ago. The New York-based group said his family does not know his whereabouts.
The Uzbek government claims that fewer than 200 people died when it put down an armed Islamic uprising, while civic groups counter that 500 or more civilians may have been killed, including women and children.
Zainabiddinov heads an Andijon-based group called Appelyatsiya.
The fergana.ru website has published a list of 19 Uzbek political and rights activists who it says have been detained since the 13 May uprising. Dozens of others have been tried and convicted of offenses stemming from the event in trials that have been heavily criticized by the international community.