New fears of Internet censorship spread in the Russian blogosphere Monday after a wireless Internet provider co-owned by Russian Technologies acknowledged blocking access to some web sites.

Moscow-based users of the Yota provider have been unable to access web sites such as Garry Kasparov’s Kasparov.ru, Solidarity’s Rusolidarnost.ru and the banned National Bolshevik Party’s Nazbol.ru over the past few weeks, bloggers and the sites’ editors said.

Access also was patchy until Sunday to the site of opposition magazine The New Times, its web editor Ilya Barabanov said Monday.

Yota denied that it was blocking those sites. But Denis Sverdlov, chief executive of WiMax operator Skartel, which runs the Yota brand, did acknowledge that Yota blocks access to sites that are classified as extremist by the Justice Ministry. Because of that, Yota users cannot open the Chechen rebel web site Kavkazcenter.com.

“In November, we got an order from prosecutors recommending that we close access to extremist sites,” he said in e-mailed comments. “Since we are a law-abiding firm, we put the order into practice.”

As for users’ lack of access to the opposition web sites, Sverdlov blamed technical difficulties that arose after Yota introduced new IP addresses to cope with the rapid growth of its customer base. “On Oct. 23, we were assigned a bloc of 65,536 IP addresses. After we put them to commercial use, we found that IT managers of some other sites could not exclude them from those IP addresses they filter,” Sverdlov said.

As proof that there was no censorship, he said President Dmitry Medvedev’s official site at Kremlin.ru was at times inaccessible as well.

Kavkaz Center was declared extremist in a 2008 court decision and appears 10 times on the Justice Ministry’s list of more than 450 items classified as extremist. The ministry’s list does not mention any of the opposition sites that have complained of being inaccessible to Yota users.

Critics say the extremism law, which was widened in 2006, is being used to silence the opposition.

It is unclear why, with the exception of Yota, most national providers do not block access to Kavkaz Center.

A representative at Yota’s technical support hot line told the Novy Region news agency on Friday that the company was blocking 29 extremist sites. The unidentified representative said Kasparov.ru was not on the list but the list had been updated a week earlier.

Bloggers, meanwhile, are rattled by an audio file posted online Sunday in which a female voice — purportedly of a Yota support representative — says Kasparov’s and Solidarity’s sites are blocked because they are on that list.

“This strongly smells of political censorship,” said Denis Bilunov, a senior member of Kasparov’s Other Russia movement.

He said the most likely explanation was Russian Technologies’ involvement in the company.

The state-owned arms and industry behemoth bought a blocking stake in Telconet in November 2008.

A spokeswoman said Russian Technologies could not immediately comment on the allegations Monday.

Skartel spokesman Anton Belkov said he would not comment beyond Sverdlov’s statement.

Skartel has been building a network providing high-speed wireless Internet service since last summer and has said it wants to become a nationwide operator covering 180 cities within three years. State corporation Russian Technologies holds a 25.1 percent blocking stake in Skartel’s parent company, Telconet.

The Internet has been called the country’s last bastion of free speech after the state brought most national television channels and influential print media under its control over the past decade. Fears of a crackdown were raised last month after a video address by police officer Alexei Dymovsky lambasting corruption unleashed a string of copycat whistle-blowers airing their complaints online. Also last month, top search engine Yandex stopped ranking popular blog posts after several entries exposed problems that embarrassed government officials.