A customer holds the newly released iPhone 6 at a mobile phone shop in Moscow, September 26, 2014. REUTERS/Maxim Shemetov Apple has suspended online operations in Russia because of instability in the ruble, Russia's currency.

"Our online store in Russia is currently unavailable while we review pricing," Apple told Bloomberg.

Russia's economy is under strain from plunging oil prices and sanctions, and the ruble has lost 20% of its value in the last week. Last night, the country's central bank raised interest rates to try and stop the slide, but it only created a very brief rally and didn't stop the longer-term trend.

Currency fluctuations make it complicated to price products properly, so Apple needs time to adjust. Last month, Apple raised prices in Russia 25% to try and counter the falling ruble. Until that point, an iPhone in Russia had become significantly cheaper than anywhere else in the country.

Russia is not a particularly important company for Apple from a business perspective — it sold only 1.6 million iPhones there in 2013, which is about 1% of all iPhone sales worldwide.

Since the online store shut down, at least one Moscow store has completely sold out of the iPhone 6 and iPad Air, according to Financial Times correspondent Jack Farchy.