"Dear users! We apologize, but access to the requested site is restricted."
This is the message some readers were dismayed to find on the evening of March 13 when they tried to access Grani.ru, a popular opposition news portal.
Grani.ru is one of three websites banned by Russian authorities under a new law that critics say aims to silence independent media and particularly the Internet, one of the last platforms for free speech in Russia.
In addition to blocking Grani.ru, the government communications regulator, Roskomnadzor, has ordered Russian providers to block access to ej.ru, the site of the online magazine "Yezhednevny zhurnal," and Kasparov.ru, a website run by opposition figure and former chess champion Garry Kasparov.
All three sites carried scathing criticism of the Kremlin's policies, including the occupation of Ukraine's Crimean peninsula by Russian troops.
The blog of Russian opposition leader Aleksei Navalny was also briefly blocked -- on the grounds that he had violated his house arrest -- but later unblocked.
"This time, authorities didn't even bother keeping up appearances and making these claims directly to us," said Aleksandr Ryklin, the editor of "Yezhednevny zhurnal." "They just instantly shut down almost all leading websites that convey opinions more or less independent from their own."
The Russian Prosecutor-General's Office ordered the other sites banned on charges of "calling for unlawful activity and taking part in mass events held with breaches of public order."
The Ekho Mosvky radio station was also asked to remove a blog by Navalny from its website, causing some providers to block the radio's entire website.
Navalny's spokeswoman, Anna Veduta, described the move as part of a Kremlin campaign to "cleanse the media space."
The crackdown comes days after the editor of Lenta.ru was summarily dismissed over its coverage of the Ukraine crisis, sparking an exodus of journalists from the top independent news site.
Lenta.ru had previously received a formal warning for publishing a link to remarks by the leader of Ukraine's ultranationalist, anti-Russian group Right Sector.
The controversial new law allows prosecutors to ban websites without court orders if these are deemed to have published calls for participation in mass protests planned without the government's authorization.
Yulia Berezovskaya, Grani.ru's general director, says she had been expecting trouble since the legislation took effect on February 1.
"Grani.ru announces and covers various rallies, both big and small, in depth," she said. "We will continue doing this. It's the actions of the regulator that are illegal, not our journalistic activities."
Grani.ru has filed a lawsuit over the blockage.
All three websites, however, can be accessed through Internet providers based outside Russia. For unclear reasons, Grani.ru is still available on several Russian providers.
Technical instructions on how to get around the ban are also making the rounds online.
Despite growing uncertainty over its future, Ryklin says ej.ru will try to operate as usual. He urges readers to support the website by continuing to visit it in defiance of the ban.
"I would be grateful if people supported Yezhednevny zhurnal simply by finding a way to continue reading it," Ryklin said. "A sustained traffic will serve us as proof. A big thanks to everyone in advance."
Written by Claire Bigg in Prague based on reporting in Moscow by Maryana Torocheshnikova