Paul Whelan, the U.S. Marine veteran who has been imprisoned in Russia for several years on what critics have said are false charges, said he fears the United States has left him behind and called inaction by successive presidential administrations "a serious betrayal."

In a phone interview from his prison cell, Whelan told the BBC he feels "abandoned" by his country, which he noted has engaged in other prisoner swaps with Russia in the last several years, including female basketball player Brittney Griner.

"It's unfathomable to me that they've left me behind," said Whelan, referencing both the current Biden administration and former Trump administration.

BBC reporter Sarah Rainsford admitted that she had never seen Whelan so "pessimistic" or "frustrated" as he appeared this week.

BIDEN PRISONER EXCHANGE FOR BRITTNEY GRINER LEAVES BEHIND MARINE VETERAN PAUL WHELAN — AGAIN

Whelan and Biden

Paul Whelan said he feels "abandoned" by the Biden administration.  (AP Photo/Alexander Zemlianichenko/REUTERS/Kevin Lamarque/File Photo)

A U.S. government spokesperson told the BBC they have initiated "multiple proposals" to the Russian government and are "constantly discussing" Whelan's situation with allies. "Not a week goes by without intensive activity," the statement continued.

Whelan said he is aware that the U.S. government has made various proposals for his release but claimed "it's not what the Russians want."

"They go back and forth, like throwing spaghetti against the wall to see what sticks. The problem is, it's my life that's draining away while they do this. It's been five years!" he said.

Whelan also criticized former President Donald Trump, noting that Russia wanted to send him back home in return for the convicted arms dealer Viktor Bout, but Trump "kept saying no."

"It's extremely stressful knowing that I could have been home years ago," he said. "It's extremely frustrating to know that they've made these mistakes. They've basically abandoned me here."

He also called the decision to leave him behind a "serious betrayal."

BROTHER OF RUSSIA DETAINEE PAUL WHELAN CALLS ON BIDEN ADMINISTRATION TO GET HIM, IMPRISONED WSJ REPORTER HOME

either Griner or Whelan

President Biden secured the release WNBA star Brittney Griner in the White House’s controversial trade for the "Merchant of Death" earlier this year. (Sofia Sandurskaya, Moscow News Agency photo via AP/AP Photo/Alexander Zemlianichenko)

While they would not describe the current standing of Whelan's case, the U.S. government spokesperson who spoke to the BBC said U.S. Secretary of State Antony Blinken remained "personally committed" to Whelan's freedom.

But last week, Vladimir Putin said any deal Russia made to secure the release of Americans had to be "mutually acceptable," further throwing Whelan's situation into unclear waters. 

"I'm extremely concerned. With each case, my case is going to the back of the line. They've kind of just left me in the dust. And at this point, this juncture, it's very concerning."

"All the promises made have been empty," Whelan added.

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In late November, Whelan's family reported that he was assaulted at a labor camp following a dispute.

A State Department spokesperson told Fox News Digital the agency was concerned over the incident. 

"We are concerned about reports that Paul Whelan was assaulted by another prisoner in IK-17 on November 28," the spokesperson said in an email. "The U.S. Embassy in Moscow has been in contact with Paul via phone and we understand he is receiving medical treatment following this incident."

The White House has not yet returned Fox News Digital's request for comment. 

Fox News' Louis Casiano contributed to this report.