Russian President Vladimir Putin said Friday that more U.S.-Russian prisoner exchanges are possible if Moscow and Washington find a compromise.

Putin spoke a day after Russian arms dealer Viktor Bout was swapped for WNBA star and two-time Olympian Brittney Griner.

Asked after a summit in Kyrgyzstan whether other prisoners could be swapped, Putin replied that “everything is possible,” noting that “compromises have been found” that cleared the way for Thursday’s exchange of Griner for Bout.

“We aren’t refusing to continue this work in the future,” the Russian leader said, making his first comments about the closely watched trade.

Despite negotiating for Griner’s release, the most high-profile American jailed abroad, the U.S. failed to win freedom for another American, Paul Whelan. The Michigan corporate security executive has been imprisoned in Russia since December 2018 on espionage charges that his family and the U.S. government have said are baseless.

U.S. officials said they did not see an immediate path to bringing about Whelan’s release, saying Russia has treated his case differently because of the “sham espionage” charges against him. Still, they said they believe communication channels with the Russians remain open for negotiations about his freedom.

US National Security Council spokesman John Kirby said: “We registered what Mr. Putin said, let’s see what he actually does.”

Putin said the U.S.-Russia talks that resulted in Thursday’s exchange didn’t touch on other subjects.

“Whether this could set the stage for a dialogue with the U.S. is a separate issue,” he said. “We didn’t set the task to move from those talks to something else, but they do create a certain atmosphere.”

On a similar note, Kremlin spokesman Dmitry Peskov said it was Russian and U.S. intelligence agencies that agreed to exchange Bout for Griner and their contacts were focused exclusively on hammering out its specifics.

“It has no impact on the overall state of bilateral ties that looks sad,” Peskov said in televised remarks.

Peskov said that “special services may continue their work if necessary,” and also noted the role of the United Arab Emirates and Saudi Arabia in helping broker the swap.

Bout, dubbed the “Merchant of Death” who provided arms for some of the world’s worst conflicts and spent over 14 years behind bars in the U.S., was seen in Russia as unjustly imprisoned after an overly aggressive U.S. sting operation.

Russian state media hailed his release, carrying footage of him talking to his family from a private jet following a swap at Abu Dhabi’s airport and then embracing his wife and his mother on a snowy tarmac in Moscow.

Speaking in an interview for RT channel with Maria Butina, who also served 18 months in a U.S. prison after being convicted of acting as an unregistered foreign agent in the United States, Bout said he was still struggling to control his emotions after his imprisonment.

He charged that the West’s long-held objective was to destroy Russia.

“The West believes that it has failed to finish us off when the Soviet Union began to collapse,” Bout said. “And our efforts to live independently, be an independent power, is a shock to them.”