10/07/2017 04:54 EDT | Updated 10/07/2017 05:00 EDT

Supporters of opposition leader Navalny rally across Russia

MOSCOW — Supporters of opposition leader Alexei Navalny rallied across Russia on Saturday, heeding his call to pressure authorities into letting him enter the presidential race with a wave of demonstrations on President Vladimir Putin's 65th birthday.

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

In Moscow, several hundred protesters, most of them young, gathered on Moscow's downtown Pushkinskaya Square, waving Russian flags and chanting "Russia will be free!" and "Free Navalny!"

Police warned the demonstrators that the rally hasn't been sanctioned and urged them to disperse, but didn't immediately move to break up the rally.

Escorted by police, mostly teenage protesters later walked down Tverskaya street toward the Kremlin, shouting "Let Navalny run!" and "Future without Putin!" Police lines blocked them from approaching Red Square, and they walked back.

The authorities' decision to refrain from disbanding the rally and allow people to march down the downtown avenue contrasted with previous rallies called by Navalny in the capital earlier this year, when police detained more than 1,000 demonstrators.

The unusual restraint probably reflected a desire to avoid a crackdown on Putin's birthday.

Navalny's headquarters called protests in 80 cities, and rallies numbering from a few dozen to a few hundred people were held in many regions. Most of the demonstrations haven't been sanctioned by authorities, but police have refrained from breaking them up, only detaining a few protesters and activists.

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 several waves of protests this year, casting a challenge to the Kremlin.

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

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

"The 86-per cent approval rating exists in a political vacuum," he said. "It's like asking a person who has been fed with rutabaga through his entire life how eatable they find it and the rating will be quite high. Listen, there are other things, which are better than rutabaga."

The sarcastic analogy demonstrated Navalny's stinging style, which has recently helped him get broad support among the young.

Navalny has worked to expand his reach with videos exposing official corruption and YouTube live broadcasts. His documentary about Prime Minister Dmitry Medvedev's alleged ill-gotten wealth has been viewed nearly 25 million times since its release in March, helping galvanize protests.

Heeding his call, tens of thousands took to the streets in dozens of cities and towns across Russia in March and June, the biggest show of defiance since the 2011-2012 anti-government protests in Russia.