Secretary of State Antony Blinken said Sunday that the United States is "actively engaged" with Russia over a possible prisoner swap to free Americans Brittney Griner and Paul Whelan, who are in Russian custody.

"The proof will be in the pudding," Blinken said in an interview with "Face the Nation," when asked whether the Russians are serious about negotiations to release Griner and Whelan. "We have to see if the engagements that we've had, the discussions that we have, produced an actual result. That's the most important thing, but we are not resting on the laurels of having put forward a proposal some months ago. We've been actively engaged over these many months to try to move things forward."

Blinken announced in July that the U.S. put forward a "substantial proposal" to Russia aimed at securing the release of Griner, a WNBA star, and Whelan, a retired U.S. Marine. Russian media has speculated that a potential exchange would involve Viktor Bout, a Russian arms dealer serving a 25-year prison sentence in the U.S. for conspiring to sell weapons to people who intended to kill Americans.

Griner has been in Russian custody following her arrest at a Moscow airport in February and conviction for possession of a small quantity of cannabis oil. She was sentenced to nine years in prison and transferred last month to a "remote" penal colony.

Whelan has been detained in Russia since December 2018, when he visited the country for a friend's wedding. He was convicted by a Russian court of espionage charges and sentenced in 2020 to 16 years in prison.

A top Russian diplomat suggested last month to reporters in Moscow that the chance of a prisoner exchange was growing, and acknowledged Bout had been offered in a possible swap, according to Russian media. But the State Department swiftly dismissed the optimism from Russia. Vedant Patel, a department spokesman, told reporters Russia has "consistently failed to negotiate in good faith," and the Kremlin's "failure to seriously negotiate on these issues in the established channel, or any other channel for that matter, runs counter to its public statements."

Still, Blinken said Sunday that since offering the "significant proposal" months ago, the Biden administration has been engaged "on a regular basis," and said the U.S. "will not stop" until the Americans are brought home.

"We've been engaged repeatedly, in any way that we can, to try to advance it and to look to see if there are different permutations that could achieve what we're trying to achieve, which is to get our people home," he said.

The secretary of state declined to provide details of a potential prison swap or talks with the Russians, but reiterated the Biden administration's commitment to freeing Griner and Whelan.

"My efforts, the efforts of the entire administration are to bring both Paul and Brittney home," Blinken said.

Russian media has reported that Moscow wants a one-to-one prisoner swap, though Blinken again declined to provide details of any discussions between the U.S. and Russia. Instead, he noted that any agreement to the release of Griner and Whelan requires Russia's cooperation.

[T]he other side gets a vote in this. It's not just what we want. It's what they're prepared to do," he said. "And this is something that we're working on almost every day."

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