By Sam Cabral
BBC News, Washington
The US has made a "substantial offer" to bring two American detainees home from Russia, its top diplomat has said.
Secretary of State Antony Blinken said he would raise the issue in a call with Russia's foreign minister next week.
Reports in US media suggest Moscow is interested in exchanging basketball star Brittney Griner for convicted Russian arms trafficker Viktor Bout.
Kremlin spokesperson Dmitry Peskov confirmed talks were ongoing but insisted no agreement had been reached.
Mr Peskov told the BBC's Moscow correspondent Steve Rosenberg that he had been surprised to hear of the reports and said he would not comment until "after an agreement has been carried out".
Despite Mr Blinken's claims that he will speak with Mr Lavrov, a Russian foreign ministry spokesperson told the state owned Tass news agency that they were not aware of any scheduled call.
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 Paul Whelan, who was convicted of espionage in 2020.
The New York Times reports that the US last month offered Russia to swap Bout for Ms Griner and Whelan, and that President Joe Biden had approved the offer.
A lawyer for Bout told Russia's Ria Novosti news outlet 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 neither she nor her husband knew 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. The 2005 film Lord of War staring Nicolas Cage is loosely based on his life.
White House spokesman John Kirby confirmed an offer had been made "several weeks ago" but noted Russia had not "favourably engaged so far".
He also acknowledged 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 had 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.
Whelan, a former US Marine, was arrested in Moscow in December 2018. He is serving a 16-year prison sentence.
The US has said it considers both Ms Griner and Whelan to be wrongfully detained by Russia.
US could swap Russia arms dealer for Griner
The curious case of the ex-marine jailed for spying
Profile: Viktor Bout
Russian strike kills five in central Ukrainian city
US economy shrinks again sparking recession fears
Appeal over mystery death of two women in Sydney
West's modern weapons stifle Russia's firepower
'My most prized possession is gone' Video
How Russia and the West are fighting for Africa's heart
Climate change killing elephants, says Kenya. Video
It's Birmingham's turn to shine – Peaky Blinders creator
Seven things you may not know about the Commonwealth
Why England is not the Premier League's top market
England-Germany Euro final will be 'a football feast'
Why are prices rising and what is the inflation rate in the US?
The isle that France and Spain share
This curious geographic transaction has been going on for more than 350 years
The surprising benefits of pruney skin
Why do our fingers shrivel in water?
The young workers who 'want it all'
The youngest in the labour market have a slew of demands
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
By Sam Cabral