MOSCOW -- The family of Paul Whelan, a Canadian-born U.S. citizen imprisoned in Russia for espionage, said Friday that he has resumed contact after unexpectedly becoming unreachable in November.

Along with WNBA star Brittney Griner, Whelan is the focus of efforts by the United States to arrange a prisoner swap with Russia.

The Associated Press and other news organizations have reported that Washington has offered to exchange Griner and Whelan for Viktor Bout, a Russian arms dealer who is serving a 25-year sentence in the U.S. and once earned the nickname the "merchant of death."

Whelan's brother, David, said in an emailed statement that Paul had called his parents early U.S. time on Friday, the first time any family member had spoken with him since Nov. 23. The family had been told that he was moved to a prison hospital, but that the reason for that was unclear because he had not spoken of health problems.

In the call, he did not explain why he was at the hospital, but said he'd been given "special dispensation" to call, indicating he had been prohibited from calling previously, David Whelan said.

"So the call at least acts as a 'proof of life' even if nothing else is explained," he said.

Alexei Tyurkin, the chairman of the prison monitoring commission in the Mordovia region where Whelan is incarcerated, said he was in the prison hospital for "planned treatment," but did not elaborate, according to state news agency RIA-Novosti.

Whelan, a former Marine who later worked as a corporate security executive, was arrested in Moscow in December 2018. His lawyer said Whelan was handed a flash drive that had classified information on it that he didn't know about.

Whelan was convicted in 2020 and sentenced to 16 years in prison.

Griner was sentenced to nine years in prison in August for drug possession after vape canisters containing cannabis oil were found in her luggage at a Moscow airport in February. Her prominence as an athlete, including two Olympic gold medals, has drawn wide attention to her case.

Asked by reporters on Tuesday whether a swap is possible before the year's end, Russia's deputy foreign minister, Sergei Ryabkov, responded: "There always is a chance."

"Regrettably, there have been a few occasions when it seemed that a decision in favour of it was about to be made, but it never happened," Ryabkov said without elaborating.