The Russian internet watchdog said Wednesday social media accounts linked to jailed Kremlin critic Alexei Navalny should be blocked, as Moscow turns up the heat on the opposition ahead of parliamentary polls.

Earlier this week Roskomnadzor blocked 49 websites linked to President Vladimir Putin's most vocal domestic critic including his main website navalny.com as well as those of Navalny's regional offices and his key allies.

The move came after Navalny's organisations were in June banned as "extremist", barring members and sponsors from running in September's parliamentary elections.

In a statement sent to AFP on Wednesday, Roskomnadzor said that social media accounts of Navalny's "extremist organisations" and their regional branches should be also blocked.

The media watchdog claimed that the accounts contained "calls to carry out extremist activity and mass unrest" and that they supported Navalny's outfits financially.

Earlier Wednesday Lyubov Sobol, a close Navalny associate, said that Roskomnadzor was seeking to block her Twitter account.

"Not even a specific tweet -- the whole account," she said on Twitter in English. "It is nothing but political censorship."

On Tuesday, Leonid Volkov, another close Navalny ally, told AFP that the media regulator also wanted to block the YouTube channels of Navalny, his campaign offices and several allies including himself.

YouTube has become one of the most visible platforms for Navalny to release his anti-corruption investigations, which are watched by millions of people.

AFP asked Google, which controls YouTube, for comment but did not receive a reply.

In a message from prison on Tuesday, Navalny urged Russians to mobilise and download a "Smart Voting" application that also allows users to read content from his now blocked main website.

Navalny's "Smart Voting" strategy calls on Russians to back candidates best placed to defeat Kremlin-linked politicians in elections.

Russia's parliamentary vote will be held from September 17 to September 19.