MOSCOW, Sept 2 (Reuters) - Russia"s communications watchdog threatened on Thursday to fine Apple and Google unless they removed an app created by Kremlin critic Alexei Navalny from their stores, the Interfax news agency reported. A Russian court declared the jailed opposition politician"s movement extremist this summer in a crackdown ahead of parliamentary elections later this month. Navalny"s allies want to use the app to organise a tactical voting campaign.