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said on Thursday that talks were underway about a possible prisoner swap between Moscow and the but there was no agreement "yet".

"A concrete result has not yet been achieved," 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 24 February.

Bout, 55, is the highest-profile Russian prisoner serving time in the US.

He inspired the 2005 arms smuggling movie Lord of WarÌýstarring Nicholas Cage.

Bout's wife Alla said on Wednesday the gunrunner knew nothing about the possible exchange.

Washington and Moscow have already engaged in one prisoner swap since .

In April, Washington exchanged former US Marine Trevor Reed for convicted Russian drug smuggler Konstantin Yaroshenko.