The Russian human-rights group Memorial has suspended its activities in Chechnya following the murder of its prominent activist Natalia Estemirova.
"We cannot risk the lives of our colleagues even if they are ready to carry on their work," senior Memorial member Alexander Cherkasov said.
Ms Estemirova, who investigated alleged abuses by Chechnya's Moscow-backed government, was shot dead on Wednesday.
The Kremlin condemned the murder, which has caused international concern.
Ms Estemirova was abducted from her home in the Chechen capital Grozny and her bullet-riddled body was found dumped in a forest a few hours later.
Memorial has accused the government of Chechnya's Kremlin-backed President, Ramzan Kadyrov, of responsibility for the murder.
Mr Kadyrov denied any involvement and promised to investigate the killing personally.