In this combination of pictures created on July 28, 2022, Russian Viktor Bout, (L) the alleged arms dealer, looks on while standing in a cell at the Criminal Court in Bangkok. US WNBA basketball superstar Brittney Griner, (C) sits inside a defendants cage before a hearing at the Khimki Court, outside Moscow. Paul Whelan, (R) a former US Marine accused of espionage and arrested in Russia, stands inside a defendant s cage during a hearing at a court in Moscow. AFP
"A concrete result has not yet been achieved," Russian foreign ministry spokeswoman Maria Zakharova said in a statement.
Moscow hoped "the interests of both parties" would be taken into account, Zakharova said.
The United States announced on Wednesday it had made a "substantial proposal" to Moscow to free two Americans held in Russia -- US basketball star Brittney Griner and former US Marine Paul Whelan.
US Secretary of State Antony Blinken declined to confirm reports that Washington was offering to trade the Americans for Viktor Bout, a Russian arms trafficker serving a 25-year sentence in the US.
Blinken said he would speak to his Russian counterpart Sergei Lavrov "in the coming days" -- their first phone conversation since Moscow sent troops into Ukraine on February 24.
Bout, 55, is the highest-profile Russian prisoner serving time in the US. He inspired the 2005 arms smuggling movie "Lord of War" starring Nicholas Cage.
Bout's wife Alla said on Wednesday the gun runner knew nothing about the possible exchange.
Washington and Moscow have already engaged in one prisoner swap since Russia launched its Ukraine offensive.
In April, Washington exchanged former US Marine Trevor Reed for convicted Russian drug smuggler Konstantin Yaroshenko.