Russia's Federal Security Service (FSB) says it has detained a U.S. citizen in Moscow over suspected spying.
The American -- identified as Paul Whelan -- was detained on December 28 and a criminal probe had been opened, the FSB was quoted as saying by the state-run TASS news agency on December 31.
The TASS report said Whelan could face between 10 to 20 years in prison if found guilty but disclosed no further details.
The announcement comes a day after Russian President Vladimir Putin said Moscow remained open to dialogue with Washington in a New Year's greeting to U.S. President Donald Trump.
The U.S. State Department said it knows about "the detention of a U.S. citizen by Russian authorities" and had been formally notified by the Russian Foreign Ministry.
"Russia's obligations under the Vienna Convention require them to provide consular access," the State Department said. "We have requested this access and expect Russian authorities to provide it."
Relations between the United States and Russia remain strained over a raft of issues including Russia's role in wars in Syria and eastern Ukraine, its alleged meddling in elections in the United States and elsewhere, and the poisoning of a Russian double agent in Britain.
At the end of November, Trump abruptly canceled a planned meeting with Putin on the sidelines of a Group of 20 summit in Argentina, citing tensions after Russian forces opened fire on Ukrainian Navy boats before seizing them and capturing 24 Ukrainian sailors.
The detention of Whelan comes weeks after a Russian woman pleaded guilty in a U.S. court to acting as an agent for the Kremlin. Maria Butina allegedly tried to lobby officials within the powerful National Rifle Association and the Republican Party in hopes of influencing U.S. policies in favor of Moscow.
The Kremlin has denied that Butina is a Russian agent and has organized a social-media campaign to secure her release.
In the past, Russia has arrested foreigners with the aim of trading prisoners with other countries.
In his annual year-end news conference on December 20, Putin said Russia would "not arrest innocent people simply to exchange them for someone else later on."