The Russian FSB has arrested a US citizens on charges of espionage in Moscow no December 28. No further details have been provided, but there has been an increase in charges of spying between the US and Russia over the past year. The US has prosecuted a number of Russians for conspiracy and other espionage-related charges, while over 100 Russian diplomats were expelled from various Western countries in response to Russia’s poisoning of one of its former spies and his daughter in the UK. Russia, in turn, responded to this incident by expelling several dozen Western diplomats. If found guilty, the American faces up to 20 years in prison. 

Source: Russian security agency arrests ‘US spy’ in Moscow – BBC News