Brittney Griner has been released from Russian prison and the two-time basketball Olympic gold medallist will be back in America in the next 24 hours, US president Joe Biden said.

At the White House, President Biden confirmed he had spoken to 32-year-old Griner, who was arrested at Moscow's Sheremetyevo International Airport on February 17 for bringing under a gram of cannabis oil into Russia in vape cartridges.

That was shortly before Russia invaded Ukraine, weakening diplomatic relations with the US, and eight-time WNBA All-Star Griner was jailed for nine years in August for drug possession and drug smuggling with criminal intent.

Griner said she made an "honest mistake", and her lawyers argued she was using cannabis for medicinal purposes to treat chronic pain sustained over the course of her career.

They said she was not aware cannabis oil was outlawed in Russia.

Reports in the United States said Griner had been freed in a prisoner exchange that has seen arms dealer Viktor Bout released into Russian hands.

President Biden said Griner had been "unjustly detained in Russia", describing circumstances she endured as "intolerable".

"Brittney will soon be back in the arms of her loved ones, and she should have been there all along," Biden said. "This is a day we've worked towards for a long time."

Biden said there had been "painstaking and intense negotiations". He said recent months had been "hell for Brittney" and stressed efforts were ongoing to free former US Marine Paul Whelan, who is in a Russian jail after being convicted in 2020 on espionage charges.

Biden said Phoenix Mercury player Griner was "in good spirits" and "relieved to be heading home" after enduring "needless trauma".

She was "wrongfully detained" in the first place, Biden said, and he added: "She endured mistreatment and a show trial in Russia with characteristic grit and incredible dignity.

"She wrote to me back in July, she didn't ask for special treatment, even though we'd been working on her release since day one."

Griner's wife Cherelle appeared alongside Biden and said: "Over the last nine months y'all have been so privy to one of the darkest moments of my life."

She said news of Griner's release left her "overwhelmed with emotions", and she offered "sincere gratitude" to Biden and his administration.

"Today it's just a happy day for me and my family," she added.