Cherkasov is serving a sentence in Brazil on charges of using fraudulent documents.

Brazil’s justice minister, Flávio Dino, said on Twitter that Cherkasov will remain imprisoned in Brazil for the time being. A Russian request for Cherkasov on allegations of drug trafficking had been conditionally approved by Brazil’s Supreme Court earlier this year, making Brazil unable to complete the U.S. request, the Brazilian Justice Ministry stated. However, the Russian request is also pending Brazil’s own spying investigation into Cherkasov.

Paulo Ferreira, one of Cherkasov’s lawyers, could not immediately be reached for comment Friday night. He told the Wall Street Journal his client is not a Russian spy.

The Justice Department and State Department did not immediately respond to requests for comment.

The Justice Department’s March complaint alleges Cherkasov acted as a type of deep-cover Russian agent called an “illegal.” Such agents operate without any known link to their home government and often build elaborate false identities.

Cherkasov lived under the alias Victor Muller Ferreira, a Brazilian citizen, but U.S. and Brazilian authorities say he was actually born in Kaliningrad, a Russian exclave sandwiched between Poland and Lithuania.

Cherkasov was seen by some as a potential bargaining chip in a prisoner swap the United States is seeking to negotiate in exchange for Wall Street Journal reporter Evan Gershkovich, who is being held in Russia on espionage allegations. Gershkovich and the Journal both say the charge is false, and the State Department says he has been wrongfully detained.