Russian crime boss Anton Kuznetsov recently celebrated his birthday with a raucous, tequila-fueled party featuring skimpy gladiators' outfits and mounds of caviar.

So far, nothing surprising for the flamboyant 26-year-old ringleader -- except, perhaps, that the carousing was held at the Serpukhov jail outside Moscow, where Kuznetsov was in pretrial custody for robbery.

The photographs have now gone viral on the Internet.

One shows a group of prisoners wearing nothing but improvised gladiators' costumes and brandishing cardboard swords, with a rather dour-looking fellow inmate donning a lion's mane.

In another shot, Kuznetsov -- who has since been convicted and is serving time in a high-security prison -- heaps red caviar on a piece of bread. He is also seen being handed McDonalds burgers and fries through a prison service hatch.

The pictures appear to have been taken with a mobile phone, one more prohibited item in Russian jails.

The case is the latest scandal to hit Russia's notoriously ill-managed prison system, which has come under increased scrutiny following the 2009 death of anti-corruption lawyer Sergei Magnitsky in pretrial detention.

A spokeswoman for the country's prison authorities said investigators had been sent to the prison and promised that the officials who facilitated Kuznetsov's birthday bash would be punished.

The threat of a stint at Serpukhov, however, has lost some of its bite.

-- Claire Bigg