The U.S. government has proposed to Russia that it release detained Americans Brittney Griner and Paul Whelan in exchange for imprisoned Russian arms dealer Viktor Bout, two sources familiar with the matter confirmed to NBC News.

Griner, a WNBA star and Olympic gold medalist, has been held in Russia since February, and Whelan, a corporate executive, has been detained in the country since 2018.

Secretary of State Antony Blinken said Wednesday that the Biden administration had made a “substantial” offer to Russia to facilitate the release of Griner and Whelan, but he did not disclose further details about the proposal.

Read the rest of the story at NBC News