The FSB did not say whether the unnamed suspect had been arrested, instead in a statement it said, "The Federal Security Service of the Russian Federation has opened a criminal case against a US citizen on the grounds of a crime under Article 276 of the Criminal Code of the Russian Federation - 'Espionage.'"
"The American is suspected of collecting intelligence on biological topics directed against the security of the Russian Federation," the statement added.
The agency did not provide further details.
US citizens detained in Russia
A number of US citizens have faced criminal charges in Russia in recent years. Both Moscow and Washington accuse each other of political arrests, and there have been several high-profile prisoner exchanges between the two countries.
In December, US basketball star Brittney Griner was freed in a prisoner swap after being sentenced to nine years in prison for carrying cartridges containing cannabis oil.
Griner was exchanged for Viktor Bout, a Russian citizen who spent 14 years in jail in the US for arms trafficking, money laundering and conspiring to kill Americans.
Paul Whelan, who was arrested in 2018 on espionage charges and handed a 16-year sentence in 2020, remains in prison in Russia.
