(Bloomberg) -- Efforts are intensifying to reach a swap deal between Russia and the US for imprisoned former US Marine Paul Whelan after last week’s exchange of WNBA star Brittney Griner at Abu Dhabi airport.

Whelan’s Russian lawyer, Vladimir Zherebenkov, told Bloomberg News that diplomacy to free the 52-year-old American is accelerating and he may be swapped ‘’within a month or two.” Whelan was sentenced to 16 years in 2020 on spying charges he denies after he was detained in December 2018 while attending a wedding in Moscow.

US National Security Advisor Jake Sullivan on Monday said “high level” talks on Whelan’s case were planned this week, though he offered no details. 

Russia handed Griner over to US officials at Abu Dhabi airport on Dec. 8 in exchange for Viktor Bout, a notorious arms dealer known as the “merchant of death” who was serving a 25-year sentence imposed in 2012. President Joe Biden’s administration spent months securing the basketball star’s release, saying publicly in July that it had made an offer for the return of both Griner and Whelan. 

But the efforts to reach an agreement for both Americans foundered despite several names put forward by Moscow to exchange for Whelan. 

Russia was willing to trade for Vladislav Klyushin, a Kremlin insider extradited to the US from Switzerland last year who has information relating to the hacking of Democratic Party servers during the 2016 presidential election, according to people with knowledge of the matter. 

Russia also asked to swap Vadim Krasikov, a former official with links to its domestic spy agency who was convicted of murder in 2021 in Germany, the people said.

“When Americans are wrongfully detained or held hostage, we take that very seriously, and we are going to do everything that we can to bring Paul Whelan home,” White House spokeswoman Karine Jean-Pierre said Dec. 15. “We’re not going to talk about steps or any conversations in public because we want to make sure that we get this done.”

Two other Russian nationals – Yury Orekhov and Artem Uss – are currently fighting extradition to the US, where they face up to 30 years in prison if convicted of allegations they helped evade sanctions by smuggling US military technology and Venezeluan oil. Orekhov was detained in Germany and Uss was arrested in Italy. Uss’s father Alexander, who is the governor of Siberia’s Krasnoyarsk region, has said the charges against his son are politically motivated.

Russia could agree to exchange Whelan for Uss, said two people in Moscow with knowledge of the matter, who declined to say if there’d been any discussion on a potential deal.

US National Security Council spokesperson John Kirby said Wednesday that Russia puts Whelan “in a different category” because of the “sham espionage charges” on which he was convicted. “We’re not going to be afraid to be innovative, in terms of trying to find other proposals that might secure his release,” Kirby told reporters.

The US special envoy who helped secure Griner’s release said Sunday he’d spoken to Whelan and assured him “we’re coming to get you.” Roger Carstens, the Special Presidential Envoy for Hostage Affairs, told CNN he was in touch with Whelan on the day after Griner was freed by Moscow.

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