Russia's media watchdog on Thursday blocked the website of opposition leader Alexei Navalny after he posted a video alleging a deputy prime minister enjoyed lavish hospitality from a billionaire tycoon.
State body Roskomnadzor has threatened to block any site distributing the video, including YouTube and Instagram, but both remain accessible in Russia.
"Roskomnadzor has blocked https://navalny.com/ at the request of (Russian oligarch Oleg) Deripaska," Navalny said on Twitter.
"The site remains accessible through some service providers, but this is temporary," he added.
Roskomnadzor confirmed the website had been added to a list of banned pages that service providers are required to block, in comments to Russian news agencies.
Navalny, who has been barred from running against President Vladimir Putin in next month's election, says the video appears to show The Russian leader's former top foreign policy adviser Sergei Prikhodko vacationing on the yacht of 50-year-old Oleg Deripaska, an aluminium magnate.
Both Deripaska and Prikhodko, who rarely makes comments to the media, denied the allegations.
The woman who Navalny said filmed the video, Nastya Rybka, describes herself as a model and has penned a book on how to seduce billionaires.
She has more than 60,000 followers on Instagram where she has posted scantily-clad or naked snaps of herself and a video of herself having sex.
Rybka's posts relating to the allegations were no longer accessible on Instagram yesterday, but Navalny's 25-minute YouTube video -- that has racked up more than five million hits since it was posted last week -- was still available.
Navalny has called for a boycott of Russia's March 18 presidential election after he was barred from running over a criminal conviction he says is politically motivated.
He is informally barred from appearing on state media and so relies on his own site and social media to spread his message, with posts drawing thousands onto the street across the country last month in support of his call for a "voters' strike," or boycott of polls.
Navalny's LiveJournal blog was blocked in March 2014 along with a number of opposition news websites after demonstrations in Moscow against Russia's annexation of the Crimean peninsula from Ukraine.
The reason given by Roskomnadzor was that he was under house arrest at the time and was not allowed to use the internet.
In January 2015, while he was still under house arrest, his entire Navalny.com site was blocked over a page allegedly containing calls to take part in illegal protests.