Rare new video has emerged showing detained American Paul Whelan, who has been held in Russia for more than four years, inside his prison camp.

The video, released by Russian state-controlled news agency Russia Today (RT), shows Whelan wearing a Russian prison uniform in different parts of the prison, with shots of him using a sewing machine and eating in a cafeteria.

At one point in the video, he tells a reporter from the Kremlin-backed media outlet, "You understand when I say that I can't do an interview, which means I can't answer any questions."

Whelan -- who has US, Irish, British and Canadian citizenship -- was detained at a Moscow hotel in December 2018 by Russian authorities who alleged he was involved in an intelligence operation.

The former United States Marine was sentenced to 16 years in prison on an espionage charge he vehemently denies. "I was arrested for a crime that never occurred," he told CNN during an exclusive interview last year. "I don't understand why I'm still sitting here."

After the release of the RT video, his brother David Whelan said, "Today was the first time I've seen what he really looks like since June 2020."

In a statement, David said the RT crew had showed up at the prison to film Whelan in May, and that "prison staff retaliated against him after he didn't participate" in an interview.

"I wish I could see Paul under better circumstances. But it was good to see him again and to see the fight remains in his eyes. It is good to know Paul remains unbowed," David said.

Earlier this month, US Secretary of State Antony Blinken spoke to Whelan, who the US government deems wrongfully detained, according to a source familiar with the call.

The US was unable to secure Whelan's release in prisoner swaps that brought home two other wrongfully detained Americans last year: Trevor Reed in April and Brittney Griner in December.

The Biden administration has put forth proposals for Whelan's release, but Russia has not responded in a substantive way, two administration officials told CNN.

This lack of response, and the wrongful detention of Wall Street Journal reporter Evan Gershkovich earlier this year, have forced the US to continue searching for another offer to put on the table, said one senior administration official -- despite the US still considering its existing Whelan proposal a live offer.

The Biden administration continues to scour the globe for offers that could entice Russia to release both of the wrongfully detained Americans, as CNN reported earlier this year. The US does not currently have any high-level Russian spies in its custody, current and former US officials say, driving the need to turn to allies for help.

In another exclusive phone call to CNN in May, Whelan said he was confident that his case is a priority for the US government but wishes it could be resolved faster. He also expressed concerns he could be left behind again if the US secures Gershkovich's release.