A Moscow court on Monday sent Russian opposition leader Alexei Navalny to jail for 20 days for calling for an unsanctioned protest, which would keep him away from a major rally this weekend, ABC News reported.

Police detained Navalny on Friday, preventing him from traveling to a rally in a major Russian city that had given its official permission to hold the gathering. Charges brought against the Kremlin's top rival relate to the upcoming rally in St. Petersburg, Russia's second-largest city and President Vladimir Putin's hometown, which has not been sanctioned.

After he announced his presidential bid last year, Navalny, arguably Russia's most popular opposition politician, inspired a grassroots campaign in Russian regions to support his nomination.

"20 days in jail. Old man Putin got so scared of our rallies in the regions and decided to make himself a little present for himself for his birthday," Navalny tweeted shortly after the ruling Monday evening.

The rally in St. Petersburg was scheduled for Saturday, which is also Putin's birthday.

Navalny's campaign late Monday called for rallies to protest his arrest in other Russian cities this Saturday.