MOSCOW, Sept 30 (Reuters) - Russian authorities on Thursday warned social media giant Facebook (FB.O) it faces a fine of up to 10% of its annual turnover in the country unless it deletes content Moscow deems illegal. Upping the ante in its standoff with U.S. Big Tech, state communications regulator Roskomnadzor told Reuters it was planning to send Facebook"s representatives in Russia an official notification saying it had repeatedly failed to remove banned information. That, it said, could lead to a fine of 5% or 10% of Facebook"s annual Russian turnover unless the situation is remedied. Facebook"s violations include failing to remove posts containing child pornography, drug abuse and extremist content, the Vedomosti daily reported separately.Facebook had no immediate comment. Moscow has increased pressure on foreign tech companies over the last year as part of a long-running push to assert greater sovereignty over its segment of the internet, including efforts to make companies store Russians" personal data on its territory. On Wednesday, Russia threatened to block YouTube, owned by Alphabet Inc. (GOOGL.O), after the video-hosting giant removed Russian state-backed broadcaster RT"s German-language channels from its site. read moreEarlier this year, Roskomnadzor wrote to Facebook and other social media firms demanding they remove posts containing calls for minors to participate in anti-government protests after the arrest of Kremlin critic Alexei Navalny. Vedomosti cited experts who estimated Facebook"s annual Russian turnover at around 12 billion roubles ($165 million). Reuters could not immediately verify that estimate. Roskomnadzor has opened 17 different administrative cases against Facebook this year for failing to delete banned content, court documents showed, with 64 million roubles owed in fines or pending. A turnover fine would dwarf those levied so far."Facebook"s administration has not paid the fines," Vedomosti cited Roskomnadzor as saying. (This story has been refiled to remove extraneous word in lede) ($1 = 72.5975 roubles)