MOSCOW (Reuters) - Russia’s FSB state security service said on Monday it has detained an American citizen suspected of spying in Moscow and has opened a criminal case against him.

The FSB said the American had been detained on Friday, but it gave no details of the nature of his alleged espionage activities. Under Russian law, espionage can carry between 10 and 20 years in prison.

A U.S. State Department representative said Russia had notified it that a U.S. citizen had been detained and it expected Moscow to provide consular access to see him.

“We have requested this access and expect Russian authorities to provide it,” the representative said, without providing details of the identity of the American or the reasons behind his detention.

The English-language service of TASS news agency named him as Paul Whelan.

David Whelan said in an email that he was Paul Whelan’s brother and said that his brother had been arrested. He declined to comment on how he learned of his brother’s detention, his work status at the time of his arrest and whether his brother lived in Novi, Michigan, as address records indicate.

There was online speculation that Paul Whelan had worked for global staffing firm Kelly Services, which is headquartered about a 40 minute-drive from Novi in Troy, Michigan.

A spokeswoman for Kelly said a Paul Whelan had worked for the company until February 2016.

“Kelly has yet to confirm whether this former employee is the same individual reported upon in the news stories,” said Kelly spokeswoman Heather Klee.

Russia’s relations with the United States plummeted when Moscow annexed the Crimean peninsula from Ukraine in 2014, and Washington and Western allies have imposed a broad range of sanctions on Russian officials, companies and banks.

Earlier this month, Russian national Maria Butina pleaded guilty in a U.S. court to a conspiracy charge in a deal with prosecutors, and admitted to working with a top Russian official to infiltrate American conservative activist groups and politicians as an agent for Moscow.