Image source, AFPImage caption, A rights group alleges that hundreds of inmates have been abused (file image)
Russian authorities are investigating allegations of torture and rape in the prison system, after leaked videos appeared to show inmates being abused.
More than a thousand videos were leaked to the human rights group Gulagu.net, which claims the footage proves hundreds of people have been tortured.
One video appears to show a naked man being abused with a stick at a prison hospital in the city of Saratov.
The BBC has not been able to independently verify the footage.
Another video appears to show a man laying face-down with his hands taped behind him, as a guard presses a boot into his back.
The films are part of a large trove of files provided by an anonymous Belarusian whistleblower who served time in the Saratov facility, Gulagu.net said.
"If the authenticity of this material is confirmed, it would be grounds for a serious investigation," Kremlin spokesman Dmitry Peskov said on Tuesday.
He added that the Federal Penitentiary Service (FSIN), which oversees Russia's prisons was looking into the matter.
An FSIN team has been sent to the Saratov prison to verify the allegations, while prosecutors are also reportedly investigating the claims.
On Tuesday night, the head of the FSIN branch in the Saratov region reportedly quit over the scandal. Alexei Fedotov submitted a letter of resignation, according to the Interfax news agency.
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"It is the first time that human rights defenders have obtained such a colossal amount of information proving the systemic nature of torture in Russia," Gulagu.net founder Vladimir Osechkin told the AFP news agency.
Mr Osechkin alleges that 200 inmates have been tortured and raped in Russian jails, with 40 depicted in videos. He has vowed to release more material in the coming days.
Tanya Lokshina of Human Rights Watch said her organisation could not verify the videos but the footage "gave grounds for strong concern."
"The problem of torture in Russian penitentiaries is very acute and the government is not doing enough to ensure effective investigation," she said.