Less than two months ago, ​​the United States won the return of former U.S. Marine Trevor Reed from Russia, where he was serving a nine-year sentence for disputed assault-related charges, by exchanging him for a jailed Russian drug trafficker.

Now, a top Ukrainian official says his country is working toward a prisoner swap to free two U.S. military veterans captured by Russian forces while serving as war volunteers in Ukraine.

But while Ukrainian President Volodymyr Zelenskyy said he would fight for their release, some experts and former U.S. ambassadors say efforts to negotiate the men’s return face far stiffer headwinds, citing a Russian desire to discourage war volunteers by punishing the men and U.S-Russian diplomatic relations being at an all-time low.

“If (the Russians’) goal is to discourage people from doing this, if their goal is to punish people who do this, they are not looking to release these people anytime soon,” said William Pomeranz, acting director of the Wilson Center’s Kennan Institute, which focuses on Russian and Ukraine research. 

ON THE MAP:Tracking Russia’s invasion of Ukraine

If the Russians do negotiate, he said, they would demand “high prices in any potential swap.”

That could mean a more protracted effort to obtain the release of U.S. Army veterans Alexander John-Robert Drueke, 39, and Andy Tai Ngoc Huynh, 27, who were captured by Russian forces after coming under fire in the northeastern Kharkiv region on June 9.

“We’ve been telling all of our extended family members that this is a marathon,” Drueke’s aunt, Dianna Shaw, told USA TODAY.

Shaw, 55, said the U.S. State Department told her family that “every single avenue of communication is being employed” to reach the Russians in an attempt to negotiate their release.

State Department spokesman Ned Price said this week officials had been in touch with authorities in Ukraine and Russia but were not provided details about the men’s whereabouts. Another spokesperson declined to comment further when reached by USA TODAY.

Will Russia agree to a prisoner swap?

The Russian military has said it considers foreigners fighting with Ukraine to be mercenaries not protected as combatants under the Geneva Conventions. 

Russian spokesman Dmitry Peskov called the men “soldiers of fortune” whose fates would be decided by a court, but he would not rule out the death penalty, he told NBC News. “They should be punished,” Peskov said.