Russia said Monday it had detained a U.S. citizen in Moscow and accused him of spying, in the latest alleged case of espionage between the two countries. The FSB, Russia’s feared domestic security service, said the American was arrested Friday “while carrying out an act of espionage.” Official Russian news outlets said the man had been identified as Paul Whelan, but no further details on his identity have been revealed. A criminal case has been opened, the FSB said in a statement, under an anti-espionage article of the Russian criminal code, which allows for sentences of as much as 20 years in prison. In his annual press conference this month, President Vladimir Putin accused Western nations of using espionage allegations to try to undermine an increasingly powerful Russia. Monday’s arrest comes days after Russian Maria Butina entered a guilty plea in Washington to acting as an illegal foreign agent. Butina faces just six months in prison, followed by likely deportation.