Biden Administration Say It 'Will Not Stop' Until Paul Whelan is Released From Russian Detention

Jim Lo Scalzo/EPA/Bloomberg via Getty, KIRILL KUDRYAVTSEV/AFP via Getty President Joe Biden, former Marine Paul Whelan

The Biden administration continues to press for the release of former U.S. Marine Paul Whelan, who as of Wednesday has been held in a Russian work camp for four years for alleged espionage.

In a statement released on the anniversary of Whelan's detention, National Security Adviser Jake Sullivan said the White House remains committed to his release.

"Today marks four years of wrongful detention in Russia for American Paul Whelan and, as the President and I have told the Whelan family, we will not stop, we will not relent, we will not cease until all Americans can celebrate Paul's return," Sullivan said in his statement.

News of Whelan's arrest broke on New Year's Eve 2018 when Russia's Federal Security Service (FSB) announced that it had detained the Michigan resident during a "spy mission." However, a U.S. government security source told PEOPLE at the time that Paul is not a secret agent for the United States.

What's more, the White House says Whelan, now 52, was subjected to a secret trial and sentenced to 16 years in a Russian penal colony based on secret evidence.

RELATED: After Brittney Griner's Release, Paul Whelan's Family Continues Fighting to Bring Him Home

In his Wednesday statement, Sullivan said that Paul and his family "recently showed the entire country the meaning of generosity of spirit in celebrating a fellow American's return while Russia continues its deplorable treatment of Paul as a bargaining chip," a nod to the recent release of WNBA star Brittney Griner from Russian custody.

President Joe Biden announced Griner's release — part of an exchange for a Russian prisoner in the United States — earlier this month. At the time, the administration noted the news was bittersweet considering Whelan remained in Russia.

In remarks about Griner, Biden said that the athlete's release was "not a choice of which American to bring home," noting that the administration also successfully negotiated for the release of American Trevor Reed earlier this year.

Speaking to PEOPLE for a recent exclusive interview, Paul's brother David Whelan said remaining hopeful amid the circumstances is a challenge.

"We saw Trevor Reed come home, and Paul didn't come home. We saw Brittney Griner come home, and Paul didn't come home. You start to wonder, 'How many more shots is the U.S. government going to be able to take, and when will the Russian government, if ever, decide that they have been given what they want in order to release Paul?'" David Whelan told PEOPLE. "It's hard to keep up your optimism, your hope for year after year, after year."

RELATED: Paul Whelan's Family Is 'Devastated' He Remains in Russia, but 'Glad' Brittney Griner Was Released

In another statement released Wednesday, Secretary of State Antony Blinken acknowledged the "four years that Paul Whelan has spent wrongfully detained, away from his family, suffering through an unfathomable ordeal."

"His detention remains unacceptable, and we continue to press for his immediate release at every opportunity," Blinken said Wednesday. "I am committed to bringing home Paul and all U.S. hostages and wrongful detainees held around the world. As the President said directly to the Whelan family, our efforts to secure Paul's release will not cease until he is back home with his family where he belongs.