A human rights group and two media outlets linked to self-exiled Kremlin critic Mikhail Khodorkovsky said Thursday they were closing under pressure from authorities after their websites were blocked.

The Russian opposition says the authorities are stepping up a campaign of intimidation against independent media and dissenters ahead of parliamentary polls in September. The Kremlin has rejected these claims.

On Wednesday evening, Russian internet watchdog Roskomnadzor restricted access to the websites of Open Media and MBKh Media, as well as the website of the Pravozashchita Otkrytki human rights group following a request from prosecutors, they said.

On Thursday, the media outlets and the rights group said they were shutting down to shield staff from prosecution.

Veronika Kutsyllo, former chief editor of MBKh Media, said the risks were "too big" for the media outlet to continue operating.

-The country is rapidly falling into some unbelievable feudal darkness- she said on Facebook.

In a statement on Twitter, Open Media said that Russian authorities did not want critical media. "But at least we tried," it said.

Both media outlets were founded by Khodorkovsky in 2017 and were critical of the Kremlin.

A number of independent media organisations and groups have been banned in Russia in recent months as part of an increasing crackdown on the opposition ahead of parliamentary elections in September. 

'Undesirable'

Open Russia, an opposition group founded Khodorkovsky, was designated an "undesirable" organisation in Russia in 2017 in line with a law targeting foreign groups accused of political meddling. In May, the group said it was closing to protect its members from prosecution.

Pivovarov, the former executive director of Open Russia, was pulled off a Warsaw-bound plane in June and is currently in pre-trial detention. The 39-year-old faces up to six years in prison for his involvement in an "undesirable" organisation.

Khodorkovsky, who owned the oil giant Yukos before he was convicted in two controversial cases and spent a decade behind bars, now lives abroad.

In July, authorities outlawed Proekt, one of the country's last independent media outlets that focused on in-depth reporting into the wealth of Russia's elite including President Vladimir Putin. Its chief editor Roman Badanin has left Russia.

The same month the media regulator blocked 49 websites linked to jailed Kremlin critic Alexei Navalny including his main website navalny.com.

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

On Wednesday, international monitors said they would not send observers to Russia for the September election because of a limit on numbers imposed by Russian authorities.