US vows to free Paul Whelan on anniversary of 'unacceptable' detention in Russia

US Secretary of State Antony Blinken on Wednesday called for the immediate release of American businessman Paul Whelan who has been detained in Russia since 2018.

"Today marks four years that Paul Whelan has spent wrongfully detained, away from his family, suffering through an unfathomable ordeal," Blinken said in a statement.

"His detention remains unacceptable, and we continue to press for his immediate release at every opportunity."

Whelan, a former marine and corporate security executive, was detained in Moscow in 2018 by Russian authorities on espionage charges. He was subjected to a secret trial and sentenced to 16 years.

"Our efforts to secure Paul's release will not cease until he is back home with his family where he belongs," Blinken added.

President Joe Biden's National Security Advisor Jake Sullivan, for his part, also said the US will not stop "until all Americans can celebrate Paul's return".

"Paul and the Whelan 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," said Sullivan in a statement.

"I am grateful for the partnership of the Whelan family as we work to reunite them with Paul," he added.

The Biden administration traded detained American basketball player Brittney Griner for a convicted Russian arms dealer Viktor Bout in a prisoner swap earlier this month.