Russia's domestic security service said on Monday it had detained an American citizen in Moscow on suspicion of spying.

A spokesperson for the State Department later told NBC News that U.S. officials had been formally notified of the detention by Russia's Foreign Affairs Ministry.

"Russia’s obligations under the Vienna Convention require them to provide consular access," the spokesperson said. "We have requested this access and expect Russian authorities to provide it."

They did not add further details citing privacy considerations.

Russian security officials said the American was detained "during a spying action" on Dec. 28 and that an investigation had been opened against him.

The security agency, known as the FSB, referenced a section of Russia's criminal code dealing with espionage, but did not provide any information about the specifics of the charges involved.

Russia's relations with the United States have been strained due to the conflict in eastern Ukraine and Moscow's annexation of the Crimean Peninsula in 2014.

Since then the U.S. and other Western countries have imposed sanctions against Russian officials, companies and banks.

The latest round of sanctions "in response to Russia's continued disregard for international norms," which includes Moscow's suspected interference in the 2016 U.S. election, were announced earlier this month.