Brittney Griner pens thank you letter, urges supporters to write to Paul Whelan

Brittney Griner late Wednesday posted an open letter thanking fans for their support and urging them to write to Paul Whelan, an American detained in Russia.

“Your letters were also bigger than uplifting me,” Griner said in a handwritten letter, which she posted to Instagram. “They showed me the power of collective hands.”

Griner said that words of hope from fans had kept her spirits up, helping “me not to lost hope at a time where I was full of regret and vulnerable in ways I could have never imagined.”

“Thank you, from the bottom of my heart,” she said. “Because of you I never lost hope.”

The WNBA star had been detained in Russia for about 10 months on charges related to illegal drugs. The U.S. swapped the WNBA star for convicted Russian arms dealer Viktor Bout on Dec. 8.

Griner on Wednesday thanked all the families who "supported the We are BG Campaign to bring me home," adding that now "it's our turn to support" other Americans wrongly detained in Russia.

Whelan, a former marine, has been held in Russia since 2018, when he was detained in Moscow by Russia's domestic intelligence agency, the Federal Security Service.

"I hope you'll join me in writing to Paul Whelan and continuing to advocate for other Americans to be rescued and returned to their families," Griner wrote.

She included a mailing address for Whelan, care of the Department of State in Washington.

Griner finished her letter: "Thank you again from the bottom of my heart. I hope your holiday season is full of joy and love."

ABC News' Ahmad Hemingway, Patrick Reevell and Mark Osborne contributed to this report.