A prominent Russian anti-torture activist has been hospitalised after being assaulted, his organisation has said.
Igor Kaliapin was attacked on Wednesday evening by an unknown man who "tried to cut his face and strangle him," according to the Kremlin-appointed Council for Human Rights.
The suspected attacker -- who reportedly claimed to be a police officer -- has been arrested, it added.
Kaliapin remains in hospital with a "suspected concussion" after the attack which took place at a private gathering at his home.
The activist is best known in Russia for founding the NGO Team Against Torture, which was dissolved in June amid a growing crackdown against "foreign agents".
The NGO had been campaigning to force Russian authorities to investigate the alleged torture of prisoners by security forces, including in Chechnya.
The human rights situation in Russia has deteriorated sharply in recent years, with many opponents arrested or forced to flee. The repression has become even worse since Russia launched its offensive in Ukraine on 24 February.