Russia’s domestic security agency said it had detained an American citizen suspected of spying in Moscow. The Federal Security Service (FSB), which is the successor to the KGB, said Monday it had caught Paul Whelan “while carrying out an act of espionage” on Friday and criminal charges were filed. Whelan faces between 10 and 20 years behind bars if he is found guilty.

No other information was revealed about Whelan or what the “act of espionage” involved but the arrest comes at a time of particularly high tensions between Moscow and Washington. It also comes in the same month as a Russian citizen, Maria Butina, pleaded guilty to a single charge of conspiring to act as a foreign agent. She admitted that she had worked with Russian officials to infiltrate conservative activist groups and politicians in the United States.

Moscow has long denied Butina was a foreign agent but has also helped launch a campaign on social media to get 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,” notes the New York Times. In his end of year news conference, President Vladimir Putin said that Russia “will not arrest innocent people simply to exchange them for someone else later on.”

News of the Moscow arrest comes shortly after Putin sent President Donald Trump a New Year’s letter in which he claimed the Kremlin is “open to dialogue” and said the relationship between the two countries is “the most important factor behind ensuring strategic stability and international security.”