"Political rallies may occur in Moscow, St. Petersburg and other places across Russia," the advisory stated. "On Oct. 27, a large march is scheduled to take place in Moscow between Pushkinskaya Square and Turgenevskaya Square."
Russia's state news agency RIA Novosti reported Thursday authorities sanctioned the opposition rally. As many as 20,000 demonstrators are expected to turn out in support of opposition leaders jailed for their role in clashes with police last year during anti-government protests.
Russian authorities blame opposition leader Sergei Udaltsov for inciting the violence. He and fellow dissident Leonid Razvozzhayev were charged by Russian prosecutors with plotting disturbances on the eve of President Vladimir Putin's inauguration in 2012 for his third non-consecutive term.
Putin's election was marred by protests. His administration has been charged by human rights groups for cracking down on his opponents.
The British government's advisory said most visits to Russia by British nationals have been "trouble-free."
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