MOSCOW, Aug 20 (Reuters) - Russian communications watchdog Roskomnadzor has demanded that Alphabet"s Google and Apple (AAPL.O) remove Kremlin critic Alexei Navalny"s app from their stores, Interfax news agency quoted the watchdog as saying on Friday. Roskomnadzor cited a Russian court ruling that found jailed Navalny"s anti-corruption foundation an extremist organisation and banned it. Navalny"s allies have published news and blogs through the app after Roskomnadzor blocked their websites.