Sergei Prikhodko told journalists that antiglobalists should not go to Russia's second city during the summit of the Group of Eight industrialized nations' leaders on July 15-17 if they were intent on causing trouble.
Violence has marred G8 summits in the past, particularly the 2001 meeting in Genoa, when demonstrators entered into running battles with riot police and one man was killed.
The aide said antiglobalists would be given "a warm reception", though he did also say that a "good reception" awaited them.
He added that the local authorities had "created all conditions for possible demonstrations."
Last week a Russian organizer of a "counter-summit" said those attending would hold their protest rallies in line with the law.
"The main aim for us is to hold a 'counter-summit' without scandals and disorder, to show that leftists and human rights movements have organizational potential," Vladimir Soloveichik said.
He said the St. Petersburg administration had given permission to hold the "counter-summit", which will finish July 15. He added that about 1,500 people including 500 foreigners, were expected to take part in the summit, which opens July 12.