Russia's Federal Security Service (FSB) said on Thursday that it has opened a criminal case against a United States citizen on suspicion of espionage, saying that the suspect was believed to be gathering "biological intelligence information."
In a statement published online announcing the move, the FSB did not say whether or not it had arrested the suspect. It did not give the name, or any other details, about the suspect.
A number of US citizens have been detained on criminal charges in Russia in recent years, with some ultimately freed in exchange for Russians detained in the United States. In December, US basketball star Brittney Griner was freed after being sentenced to 9 years in prison on drug charges.
However, espionage cases are seen as especially fraught, with Russian security services often unwilling to release those it accuses of being spies.
Russia has so far refused to swap US Marine Corps veteran Paul Whelan, who was arrested by the FSB in 2018 on espionage charges and sentenced to 16 years in prison in 2020.