The brother of a US citizen arrested on Friday for spying in Russia has told BBC News he is innocent and was in Moscow to attend a wedding.
The family of ex-Marine Paul Whelan, 48, learnt of his arrest on Monday from news reports after wondering why they had not heard from him for days.
His twin brother David Whelan says he knew Russia well and cannot believe he would have broken any laws.
Russia's FSB state security agency says he was "caught spying" in Moscow.
The Michigan man was charged with the crime of espionage, for which he could be sentenced to at least 10 years in prison.
The US state department has requested consular access after being notified by the Russian authorities of the detention.
Spy scandals have erupted between Russia and America at regular intervals since the Cold War, while Russia's actions in Ukraine since 2014, and allegations of Russian meddling in the 2016 US presidential election, have seen relations plummet.
He had been attending the wedding of a fellow former Marine to a Russian citizen and had planned to visit Russia's second city, St Petersburg, in addition to Moscow.
Paul Whelan, his brother said, has been visiting Russia for business and pleasure since 2007, working in corporate security, with automotive industry components firm BorgWarner his most recent employer.
As well as serving in the US military, he has worked in law enforcement in the past.