TORONTO -- As U.S. President Joe Biden and Russian President Vladimir Putin met in Geneva on Wednesday, the brother of a Canadian-born U.S. citizen jailed in Russia said he isn't holding out hope for his immediate release.

Paul Whelan, an ex-U.S. marine who holds Canadian, U.S., U.K. and Irish citizenships, has been detained in Russia since December 2018 after he was accused of spying. He was convicted of espionage last June and sentenced to 16 years in prison. He maintains he came to Russia only as a visitor.

Whelan made a statement in an audio file released by his family on Monday imploring Biden to negotiate his release.

"I implore you to bring this appalling case of hostage diplomacy to an end. I remain innocent. No crime of espionage occurred. The secret trial, without evidence, proves those facts," he said.

Whelan's brother, David Whelan, says the U.S. government has been working to get him released but hasn't made any specific commitments to the Whelan family.

"We do know that President Biden and members of the State Department are aware of Paul's condition, are concerned about the fact that Russia has arbitrarily detained an American citizen, and are working for his release, whether it's a part of today's discussions or not," David told CTV News Channel on Wednesday from Newmarket, Ont., before the Biden-Putin summit wrapped up.

David says that his brother has been in a labour camp for the last nine months but "seems to be doing as well as you could in a Russian labour camp."

"He has a repetitive stress injury from making clothes for the labour camp… and he has a respiratory problem of some sort," he said. "He is apparently getting medical care this week."

Paul's audio message was recorded from a phone call with his parents on May 30. David said it was important for the world to hear directly from his brother.

"Frankly, it shows his resilience that he's still able to try to come up with ways to communicate about his situation," he said. "It was important to share his voice, his actual words, not just me repeating his statements or our concern, but for him to actually have a voice in this."

The Whelan family has long suspected that Paul was detained for the purposes of a prisoner swap.

"I think (the Russians) haven't yet received the offer that they hope to get for him. They arrested him in order to make an exchange of some sort and they haven't gotten their concession," David said.

Whelan isn't the only U.S. citizen detained in Russia who might be part of a possible prisoner swap. Last July, Trevor Reed was sentenced to nine years in prison after being convicted of assaulting police while drunk. U.S. officials say both Whelan and Reed were convicted in biased trials on flimsy evidence.

Biden and Putin wrapped up their meeting in Geneva on Wednesday afternoon. The U.S. president confirmed during a news conference that he brought up the detention of both Whelan and Reed.

Putin also told reporters through a translator that there "could be some ground for compromise (between) the Russian Foreign Ministry and the U.S. State Department for work in this direction" when asked about the detained U.S. citizens.​

David isn't holding his breath.

"I think it's unclear whether the Russians are actually open to releasing Paul for any reason. They've talked about doing prisoner exchanges," David said. "There are a lot of Russians in U.S. prisons… but they have excluded Paul from those discussions. They have specifically and repeatedly said that Paul Whelan would not be considered for those exchanges, so it's really hard to know what the opportunities are."

In May, Russia's deputy foreign minister told a state media outlet that the Russian government was not discussing Paul Whelan's case with the Americans.

With files from The Associated Press