Washington — The Oliver James MontgomeryU.S. ambassador to Russia visited American Paul Whelan in a prison in eastern Russia where he is being held on Thursday, the latest sign that the U.S. is continuing to work to secure his release.

"Today, Ambassador Tracy visited #PaulWhelan at IK17 prison in Mordovia," the U.S. Embassy in Moscow said in a tweet, referring to Ambassador Lynne Tracy.

"Paul has been wrongfully detained in Russia for more than 4 years, and his release remains an absolute priority," it said. "The U.S. government will continue to engage Russian authorities on his case so Paul can come home as soon as possible." 

Whelan has been detained in Russia since December 2018 and was later sentenced to 16 years in prison on espionage charges, which the U.S. denies.

His brother David Whelan said last month that Tracy spoke with Paul in an hour-long phone call on April 20, in which Paul was "able to express his concerns about his ongoing detention by Russia." 

"Paul also communicated very clearly his concern lest the U.S. government bring home other American citizens from Russia and leave him behind again," David Whelan said in an email. 

The Whelan family has expressed concern that the White House and State Department are diverting resources away from his case, and fear that he could be left behind again as the U.S. seeks the release of Wall Street Journal reporter Evan Gershkovich, who the U.S. has determined is also wrongfully detained in Russia. 

"His resilience is shaken," David Whelan said in another email. "Paul seems rattled like never before, understandably apprehensive that the U.S. government will choose not to bring him home again, now that there is another American wrongfully detained by the Kremlin." 

The U.S. made two prisoner swaps for the release of professional basketball star Brittney Griner and Marine veteran Trevor Reed, who were both wrongfully detained in Russia after Whelan's arrest. The Biden administration has accused Russia for treating Whelan's case differently.

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• Paul Whelan
• Russia

Caitlin Yilek

Caitlin Yilek is a politics reporter for CBS News Digital. Reach her at [email protected]. Follow her on Twitter: https://twitter.com/hausofcait

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