Eight reporters from the Russian News Service said they could not work under new rules that required them not to interview or mention opposition leaders such as Garry Kasparov and to ensure 50% coverage of "positive news".

In an interview with the German newspaper Welt am Sonntag yesterday, Mr Kasparov praised the German chancellor, Angela Merkel, for being the first European leader to confront Vladimir Putin when she complained at last week's EU-Russia summit that opposition leaders had been prevented from travelling to the Volga city of Samara for a demonstration coinciding with the summit.

"This was the first time that a European leader delivered such a serious reprimand to Putin and with that she put Putin in an extremely awkward position," he said. "After all, he's not used to being so blatantly criticised. Merkel was very right to confront him about the human rights situation in Russia."

He added: "Samara was a turning point ... [it] is the heartland of Russia. It was here that she delivered her verdict."

With the exception of one vibrant radio station, Ekho Moskvy, Russia's broadcast media has largely been transformed into a propaganda machine since Mr Putin came to power in 2000.

Yesterday, about 300 demonstrators gathered in Moscow to protest against the increasing censorship.

Artyom Khan, one of the reporters who resigned, said restrictions were introduced when new management was imported last month from Channel One, the state television station that documents Mr Putin's every move.