MOSCOW — In a challenge to President Vladimir Putin on his 65th birthday, protesters rallied across Russia on Saturday, heeding opposition leader Alexei Navalny’s call to pressure authorities into letting him enter the presidential race.

Police allowed demonstrators in Moscow to rally near the Kremlin in an apparent desire to avoid marring Putin’s birthday with a crackdown. A bigger rally in St. Petersburg, Putin’s hometown, was disbanded by police after protesters blocked traffic and tried to break through police cordons.

The rallies came as Navalny himself is serving a 20-day jail term for calling for an earlier unsanctioned protest.

In Moscow, several hundred protesters, most of them students, gathered on downtown Pushkinskaya Square, waving Russian flags and chanting “Russia will be free!” and “Let Navalny run!”

Police warned them that the rally wasn’t sanctioned and urged them to disperse, but let the protest continue for hours without trying to break it up.

Mostly teenage protesters later walked down Moscow’s Tverskaya Street toward the Kremlin, shouting “Putin, go away!” and “Future without Putin!”

Police lines blocked them from approaching Red Square and they turned back. Several hours later, some made a new attempt to march on the Kremlin, shouting “Putin thief!” and briefly tried to block traffic.

“We battle for Russia to be free from Putinism. Because the power we have now is feudal, we have no freedom of speech, no freedom of choice,” said protester Stepan Fesov.

The authorities’ decision to refrain from breaking up the Moscow protest contrasted with a more forceful response to previous Moscow rallies called by Navalny, when police detained more than 1,000 demonstrators.

Police also didn’t intervene at first with a bigger unsanctioned rally in St. Petersburg, where over 1,000 gathered at Marsovo Pole park and then marched across the city, cutting traffic and chanting “Russia without Putin!” and “Putin, retire!”

Shortly afterward, police broke up the demonstration, detaining dozens after some tried to break through police lines. Police said they will face fines for blocking traffic.

“Putin has been in charge since I was born,” said Dmitry Samokhin, 18, who was among the protesters in St. Petersburg. “The country is mired in stagnation and I want to see changes.”

Navalny’s headquarters called protests in 80 cities. Most were not sanctioned by authorities, but police largely refrained from dispersing the rallies that drew from a few dozen to a few hundred people. The Siberian city of Yakutsk saw a tough police response, with a few dozen demonstrators reportedly detained.

Navalny has declared his intention to run for president in the March 2018 election, even though a criminal conviction that he calls politically motivated bars him from running. The 41-year-old anti-corruption crusader has organized waves of protests this year, raising the pressure on the Kremlin.

Putin hasn’t yet announced whether he would seek re-election, but he’s widely expected to run. With his current approval ratings topping 80 percent, he is set to easily win another six-year term in a race against torpid veterans of past election campaigns, like Communist Party chief Gennady Zyuganov.

Navalny argues that the high level of support for Putin comes from the lack of real political competition and urged supporters to help him get registered.

“(Putin’s) 86 percent approval rating exists in a political vacuum,” he said. “It’s like asking a person who has been fed rutabaga his entire life how eatable they find it and the rating will be quite high. Listen, there are other things that are better than rutabaga.”

The sarcastic analogy demonstrated Navalny’s stinging style, which has helped him win broad support among the young.

Navalny has worked to expand his reach with videos exposing official corruption and YouTube live broadcasts.