The Biden administration has made a “substantial offer” to bring two American detainees home from Russia, the US secretary of state has said.
Reports have suggested Moscow is interested in exchanging basketball star Brittney Griner for convicted Russian arms trafficker Viktor Bout.
Secretary Antony Blinken said he would raise the matter in a call next week with Russia’s foreign minister.
Mr Blinken and Sergei Lavrov have not spoken since the war in Ukraine began.
Both the White House and the Department of State declined on Wednesday to disclose details of the proposed deal.
According to CNN, the US hopes to trade Bout for Ms Griner and fellow American detainee Paul Whelan.
The New York Times reports that the US last month offered Russia to swap Bout for Ms Griner and Mr Whelan, and that President Joe Biden had approved the offer.
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A lawyer for Bout told Russia’s Ria Novosti news outlet that he could not comment on the reports of a possible exchange with his client, but “this could change soon”.
Bout’s wife, Alla, told Ria Novosti that neither she nor her husband knows anything about plans for such a prisoner trade.
The arms dealer, dubbed the merchant of death, is currently serving a 25-year prison sentence in the US on charges he attempted to sell weapons to a Colombian rebel group to kill Americans.
White House spokesman John Kirby confirmed an offer had been made “several weeks ago”, but noted Russia “hasn’t favourably engaged so far”.
He also acknowledged that negotiations to secure the duo’s release were “delicate work” and the decision to go public with word of the proposal was a risky one.
“It’s not going to help us get them home if we’re negotiating in public,” he said.
Mr Kirby added that a White House official had spoken with the Whelan and Griner families ahead of Mr Blinken’s announcement, and they would speak again over the next 48 hours.
The deal would be the first concrete action announced by the US government with regard to the release of Ms Griner.
The 31-year-old has been in custody since February after Moscow airport officials found cannabis oil in her luggage, while she was returning to the US after playing in Russia.
At her drug possession trial on Wednesday, Ms Griner said the officials had made her sign documents, but “no-one explained any of it to me”.
She also said she received neither an explanation of her rights nor access to a lawyer in the initial hours of her detention, and that she had to use a translation app on her phone to communicate.
The two-time Olympic gold medallist has pleaded guilty to the drug charges against her, but denied deliberately breaking the law, saying she had packed her bags in a rush.
“I still don’t understand to this day how [the vape cartridges] ended up in my bags,” Ms Griner said.
“With them being accidentally in my bags, I take responsibility, but I did not intend to smuggle or plan to smuggle anything into Russia.”
With her detention extended through December, her slow-moving trial will continue in August.
Mr Whelan, a former US Marine, was arrested in Moscow in December 2018.
Convicted of being an American spy in 2020, he is serving a 16-year prison sentence.
The US has said it considers both Ms Griner and Mr Whelan to be wrongfully detained by Russia.