The 2018 World Cup hosts Russia were grappling on Thursday with a new football hooliganism scandal after the unruly behaviour of fans who threw fireworks on the pitch forced the abandonment of a top-flight cup match.
The referee called off fourth round Russia Cup match between Dinamo Moscow and their local rivals Torpedo Moscow 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 fan groups on the streets around the stadium before the match late Wednesday. Another six were arrested after the match was stopped.
"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.
Russian fan behaviour is already under the microscope after the unruly behaviour of supporters at the Euro 2012 football championships when Russian fans violently clashed with Polish counterparts.
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.
Topedo, 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.