Kremlin spokesman Dmitry Peskov said on Tuesday that any talks on a possible prisoner exchange involving U.S. basketball star Brittney Griner needed to be discreet and that “megaphone diplomacy” would not achieve results.

Secretary of State Antony Blinken said on Wednesday that Washington has made a “substantial offer” to Moscow to release American citizens held in Russia. A source said that the United States was willing to exchange convicted arms trafficker Viktor Bout, known as the “Merchant of Death.”