The International Helsinki Federation for Human Rights said on 5 December that Osman Boliev, head of the human rights NGO Romashka, was detained on 15 November at his home in Khasavyurt and remains in custody.
The group said in a statement that a hand grenade was planted on him, serving as grounds for charging him with illegal possession of weapons.
A letter sent to the top prosecutor in Daghestan and other Russian officials asked for Boliev's immediate release and a criminal case to be opened against local police.
The group said the activist had been investigating the 2004 kidnapping of a local man and had sent his case to the European Court of Human Rights.
RFE/RL Caucasus Report
SUBSCRIBE For weekly news and in-depth analysis on Armenia, Azerbaijan, Georgia, and Russia's North Caucasus by e-mail, subscribe to "RFE/RL Caucasus Report."