MOSCOW (REUTERS) - Russian authorities are looking into video footage leaked on the Internet which appears to show inmates at a prison in the Saratov region being brutalised and sexually assaulted, the Kremlin said on Tuesday (Oct 5).

The footage was published online by Gulagu.net, a rights group focused on alleged abuses in the Russian prisons system.

It said it had received a massive leak of documents, photos and videos which proved that hundreds of people across the Russian prison system had been tortured and raped.

It said it would release more material in the coming days.

Reuters could not independently authenticate the footage.

The Kremlin said the Federal Penitentiary Service (FSIN) was looking into the matter.

"If the authenticity of this material is confirmed, it would be grounds for a serious investigation," said Kremlin spokesman Dmitry Peskov.

Russian news agencies reported that FSIN had sent a team to the prison in the Saratov region, around 700km south-east of Moscow, to try to verify the allegations and that the General Prosecutor's office was looking into the matter too.

Six former inmates and a former prisons inspector told Reuters earlier this year about life inside the jail in a different region where Kremlin critic Alexei Navalny is being held for parole violations he denies.

They spoke of regular beatings by guards, sexual assaults, severe psychological pressure and medical neglect.

Russian law says inmates must not be treated in a way that is "harsh" or "abases human dignity."

If a prison official abuses his position, he can be jailed for up to a decade.