MOSCOW—Russian authorities on Thursday warned social media giant Facebook it faces a fine of up to 10 percent 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 percent or 10 percent 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 …