Zenit fans riot after winning Russian title
Fans invaded the pitch and tore down the goalposts after Zenit crushed Rostov 5-0 on Sunday to secure the title and qualify for the group stages of next season's Champions League.
At least 1,000 Zenit supporters - who have one of the worst reputations for violence in Russia - then tried to march down the city's main thoroughfare Nevsky Prospekt but were blocked by riot police, Reuters witnesses said.
State television showed pictures of several dozen riot police, backed by two armoured cars, running towards fans.
Reuters witnesses saw police beat and detain several fans who threw flares and bottles.
A spokesman said police prevented around 200 fans from marching down the city's main street but denied there were clashes.
He added one policeman suffered a minor head injury after falling.
Last month Russian news agencies reported that several fans from Croatian club Hajduk Split were beaten up by Zenit rivals at a hotel in St Petersburg ahead of a Europa League game.