Masked attackers ransacked the offices of one of the last rights groups active in Russia's Chechnya region on Wednesday as crowds of pro-government demonstrators looked on, activists said.
A gang of youths broke down the door of the office in Grozny and "started smashing everything", forcing staff to flee through windows, the prominent rights group Committee Against Torture said on its Twitter account.
"I jumped from the second floor, then our intern jumped. He almost fell but we caught him. All this was watched by police," staff member Albert Kuznetsov told opposition news website Zona.media.
The attackers also bashed the organisation's car with sledgehammers.
The incident follows years of harassment and murders of human rights activists and journalists investigating torture, kidnapping and war crimes in the tiny North Caucasus province where Russia has been fighting nationalist and Islamist rebels for 20 years.
The rights group's leader Igor Kalyapin told RIA Novosti state news agency that staff could not get through to police initially and that officers did not arrive for several hours.
"For two hours as the raid continued, the police never appeared on the scene," he wrote on Facebook.
The attacks came after a crowd of protesters gathered outside the offices in Grozny with placards attacking Kalyapin.
Kalyapin wrote on Facebook that the attackers also took away unspecified documents from the office.
Several hours after the attack, Chechen strongman Ramzan Kadyrov told journalists "an investigation is going on, and based on the results, we will take the measures laid out by the law".
The local interior ministry said it detained 30 of those protesting against the rights group.
Kadyrov said the protesters were relatives of a Chechen businessman called Dzhambulat Dadayev, who was killed April in Grozny in a special operation carried out by officers from another region.
Chechnya's leadership has condemned Dadayev's killing, with Kadyrov saying his officers have the right to shoot any Russian carrying out such an operation without his permission.
Kadyrov said protesters were questioning why the Kalyapin's group did not investigate this incident "if they fight torture by law enforcement authorities".
The Committee Against Torture's office was also torched in December after it criticised Kadyrov for urging collective punishment of the families of Islamist insurgents.
Activists from the group appeared in a documentary released last month by an organisation run by Mikhail Khodorkovsky, a former oligarch and Kremlin foe, alleging abuses and corruption by Kadyrov.
The rights group posted CCTV footage on Wednesday of the attackers using a blowtorch to open the door of a flat used by activists.
Investigative journalist Yelena Milashina also posted a video of a masked attacker pulling a security camera from the office's balcony and stamping on it as the crowd whistled and cheered.
Grozny state television reported that members of the public had gathered for a "spontaneous picket" of the group's office.
Protesters highlighted the "double standards" of the rights group and said its activities were carried out "to order", local state television said, implying those orders were from the West.
Russia's justice ministry has listed the Committee Against Torture as a "foreign agent" under a controversial law covering groups with political activities that receive foreign funding.