Russia said Friday it hoped the United States will return notorious Russian arms trafficker Viktor Bout in a prisoner swap, after American basketball star Brittney Griner was transferred to a penal colony.

"I would like to hope that the prospect (of an exchange) is not only still a topical issue, but that it is being strengthened, and the moment comes when we get a concrete agreement," Deputy Foreign Minister Sergei Ryabkov told reporters in Moscow, according to the state-run news agency RIA Novosti.

The US athlete was arrested at a Moscow airport in February and handed nine years in prison in August for possessing vape cartridges with a small quantity of cannabis oil.

Her lawyers confirmed Thursday she had been transferred to the central region of Mordovia.

Last week US President Joe Biden voiced hope that Russian leader Vladimir Putin would negotiate "more seriously" to free Griner.

Observers have suggested that Griner could be traded for Viktor Bout, a Russian arms trafficker serving 25 years in prison on a 2012 conviction.

Another American jailed in Russia, retired US Marine arrested in December 2018 and accused of spying, Paul Whelan is also slated for a possible exchange, observers say.