The existence of the gangs was first reported by the Vremya Novostei newspaper after a group of teenagers in southwest Moscow stabbed to death Sergei Nikolayev, a well-known chess player from Russia's Republic of Yakutia, on October 20.
The newspaper also said that the teenagers went on to attack an Uzbek street cleaner, Rustam Gulimov, seriously injuring him.
Police subsequently arrested six teenagers aged between 14-18 in connection with the assaults. One of them had video-recorded the attacks and uploaded them onto the Internet, the newspaper reported.
The detainees later told police that between 15 and 20 of them had met on October 20, drunk some beer, and dispersed all over the city, carrying out attacks on people they deemed "non-Russians". A total of 27 racially motivated attacks were registered in Moscow on that day.
On November 8, Russian media reported that two teenagers had been detained in connection with a series of 25 murders carried out between October 2006 and April 2007.
However, a spokesman for investigators, Mikhail Ionkin, said that the young people had been in custody since April. He refused to give further details of the case or to speculate on the motivation behind the alleged murders.
The arrests are widely believed to have been connected to investigations into 37 murders confessed to by a Russian student, Artur Ryno, 18, arrested after stabbing an Armenian national to death in April in Moscow.
Ryno was allegedly assisted in the murders, yet to be confirmed by police, by another student, Pavel Skachevsky, also aged 18. Skachevsky has denied any involvement, however.
Speculation continues in the Russian media as to the exact number of murders committed by the teenage gangs, with some sources saying the final total could be as high as 50 this year alone.
Russia has seen an explosion of racially-motivated attacks in recent years, and the Vremya Novostei paper expressed on Friday concern that leading politicians are remaining silent over rising xenophobic trends in Russian society, saying: "Today when 'the unification of the nation' is declared a priority, it would be politically inconvenient to admit the obvious nationalistic sentiments in the country".