Attackers have set alight the office of one of the few human rights groups active in Chechnya after it criticised the Russian republic’s president.
They attacked the Joint Mobile Group (JMG) office in the Chechen capital, Grozny, on Saturday evening.
Nobody was hurt but there are concerns over the safety of two activists.
The JMG had criticised Ramzan Kadyrov after he called for collective punishment of the families of rebels behind a recent attack in Grozny.
Islamist rebels launched an assault on the city on 4 December, killing 14 police officers. Nine militants also died.
In the wake of that attack Kadyrov called for relatives of the militants to be punished. Not long afterwards masked men burnt down homes in the village of Yandi.
JMG founder Igor Kalyapin formally complained in Moscow last week about Mr Kadyrov, after which the Kremlin-backed leader publicly accused the NGO official of “backing criminals”.
A demonstration was held on Saturday in Grozny against the human rights group, after which armed men tried unsuccessfully to enter its office before setting it on fire.
The extent of the damage to JMG’s office is unclear.
Video published by Russian independent newspaper Novaya Gazeta shows a fire engine outside a four-storey building, which does not look seriously damaged.
The two activists, Dmitry Dimitriyev and Sergei Babinets, reportedly called police to their flat on Sunday to make a complaint about the arson attack in the office next door.
Instead, the police searched the two men and confiscated their laptops, cameras and phones, Mr Kalyapin wrote on Facebook (in Russian).
Their phones were later returned but when Mr Dimitriyev tried to leave the building he was physically prevented from doing so, the JMG founder added.
A Chechen police source denied harassing the JMG staff, accusing them of spreading misinformation.
He told Russia’s Interfax news agency the fire was accidental.
JMG is part of Russia’s Committee Against Torture, a non-governmental organisation which has been active for 14 years and largely relies on foreign grants for its investigations.