Russia's main opposition television channel said Wednesday that viewers across the country had their access cut after senior officials reacted furiously to a poll on World War II. Several providers dropped the independent Internet and cable channel Dozhd (Rain) from their television packages after criticism over a poll on the siege of Leningrad. Lawmakers earlier this week condemned the poll as unpatriotic and asked the prosecutor-general to investigate the channel for extremism, which is punishable by imprisonment. The Russian Association of Cable Television, an industry association, has urged providers to drop the channel, which President Vladimir Putin's spokesman said Wednesday had "crossed all the limits of what can be tolerated." Dozhd conducted a phone-in poll on Sunday asking Russians whether Leningrad should have been surrendered in order to save hundreds of thousands of lives. The poll appeared on the eve of Monday's 70th anniversary of the lifting of the siege of Leningrad, one of the darkest pages in Russian history which saw at least 800,000 people die of hunger. The channel swiftly pulled the poll and apologised after criticism, with editor-in-chief Mikhail Zygar saying in an open letter to viewers that it "did not intend to insult anyone." However, Dozhd said on Wednesday it had been dropped by several cable operators including Dom.ru and AKADO, which is controlled by Kremlin-friendly tycoon Viktor Vekselberg. "It happened in eight large cities across Russia today," a channel representative told AFP after Dom.ru pulled the plug. NTV-Plus, a leading satellite broadcaster controlled by state energy giant Gazprom, said it too was removing Dozhd because the Leningrad siege issue could harm its reputation. Kremlin rights council 'concerned' Liberal commentators and staff at the opposition channel, which is known for its critical coverage of Putin and interviews with opposition leaders, called the pressure politically motivated. The Kremlin has tightened control over all major media outlets since Putin came to power in 2000. Since returning to the Kremlin for a third term last year, Putin has ramped up patriotic rhetoric in a bid to rally support after huge protests against his rule. The Kremlin's Human Rights Council said it was "extremely concerned" by the call from the president of the Association of Cable Television, Yury Pripachkin, for providers to drop the channel. "No registered media outlet can be closed or taken off the air without warnings from (telecoms regulator) Roskomnadzor and a court decision," the rights council said in a statement. Prominent Russians also expressed concern. "What is so awful about the siege question on Dozhd?" said film director Alexei Gherman Jr. in a blog post. "Where are you taking the country? (On the path) to North Korea? To the Middle Ages?"