MOSCOW — A United States citizen has been detained in Moscow on espionage charges, Russia’s domestic security agency announced in a brief statement on Monday.
The statement said that an American identified as Paul Whelan had been taken into custody on Friday on suspicion of spying. The statement implied that he had been caught red-handed, saying that the arrest had occurred “during an act of espionage.”
A criminal case has been opened against Mr. Whelan, said the statement from the F.S.B., or Federal Security Service, which gave no other details.
“We are aware of the detention of a U.S. citizen by Russian authorities,” a press officer for the State Department in Washington said by email on Monday. “Russia’s obligations under the Vienna Convention require them to provide consular access. We have requested this access and expect Russian authorities to provide it.”
Further details about the case could not be provided because of privacy concerns, the press officer said.
The arrest comes during an extended period of tension in relations between Moscow and Washington, particularly over the issues of election hacking and influence peddling.
A Russian citizen, Maria Butina, 30, pleaded guilty this month in Federal District Court in Washington to a single charge of conspiring to act as a foreign agent. She admitted to being involved in an organized effort, backed by Russian officials, to try to lobby influential Americans in the National Rifle Association and the Republican Party.
She faces six months in prison, most likely followed by deportation.
The Russian government, while strenuously denying that Ms. Butina is a Russian agent, has organized a social media campaign to win her release. While there is no apparent connection between her case and Mr. Whelan’s, in the past, Russian authorities have arrested foreigners with an eye toward trading prisoners with other countries.
During his annual year-end news conference in Moscow on Dec. 20, President Vladimir V. Putin said, “the law of retaliation states, ‘An eye for an eye or a tooth for a tooth,’ ” but he added, “we will not arrest innocent people simply to exchange them for someone else later on.”
He also said that Ms. Butina had not been following any instructions from the Russian government or its agencies, and noted that she was fighting to avoid prison.
“I do not understand why they put her there in the first place,” Mr. Putin said. “There were simply no grounds for it.”