The 2018 World Cup hosts Russia grappled on Thursday with a new football hooliganism scandal after fans forced the abandonment of a top-flight cup match by throwing fireworks and smoke bombs on the pitch.
The referee called off the fourth round Russia Cup tie between Dinamo Moscow and their local rivals Torpedo in the 51st minute amid chaotic scenes with parts of the pitch blanketed in smoke and fireworks crackling on the turf.
Police said in a statement that 20 fans were arrested as fights broke out between rival Moscow fan groups on the streets around the stadium before the match late Wednesday. Another six were arrested after the match was stopped.
The Russian Football Union (RFU) said in a statement that it was bringing forward a meeting of its disciplinary committee to Friday to decide sanctions that would likely see hosts Torpedo forfeit the match and face a hefty fine.
"Fights before going into the stadium, the pitch pelted with fireworks and endless vulgar chants from the stands. What happened yesterday had nothing to do with football," said respected sports daily Sovietsky Sport.
The incident is a huge embarrassment for Russia days before it hosts a top FIFA delegation including the world football body's president Sepp Blatter for a glitzy ceremony to announce the final list of the host cities for the 2018 World Cup.
The head of the Russian Football Union's inspection committee Alexei Spirin said the incident showed the need for separate laws in Russia against football hooliganism that would allow criminal punishment for misbehaviour.
"These were not just simple fireworks and smoke bombs -- what the Torpedo fans threw were real mini-bombs. If one of those had hit someone on the head the consequences could have been very serious."
Underlining Spirin's concerns about the lack of proper anti-hooliganism laws in Russsia, all those detained by the security forces got away with relatively light punishments.
A Moscow court handed two of the accused short administrative jail terms of three and five days each, one person was fined 1,000 rubles ($32) and 14 others a mere 500 rubles ($16), the RIA Novosti news agency reported.
Russian fan behaviour is already under the microscope after the unruly antics of supporters at the Euro 2012 football championships when Russian fans violently clashed with Polish counterparts.
As a sanction UEFA had originally imposed a six-point deduction on Russia for the 2016 qualifying competition -- suspended until the end of the play-offs -- as well as a 120,000 euros ($150,000) fine.
After an appeal by Russia, UEFA ruled in August that Russia no longer faced a potential points penalty but instead slapped it with the sanction of playing the first three games behind closed doors -- again suspended until the end of the qualifiers. The fine was unchanged.
Hosts Torpedo were trailing Dinamo 1-2 when the violence broke out and are now expected to forfeit the match, with Dinamo automatically going through to the next round of the Cup.
Torpedo, whose fans threw the fireworks on the pitch, also risk having to pay the Russian football authorities a heavy fine. But it is not clear what sparked the tensions with fans interviewed by state television blaming a "provocation" by a third party.
Huge tensions exist in Russia between supporters of the top teams, who often group into hard-core fan gangs.
A cup clash earlier this week in the western exclave of Kaliningrad between Baltic rivals Zenit Saint Petersburg and Baltika of Kaliningrad sparked such concerns that police threw a security blanket over the whole city centre.