WASHINGTON >> The Biden administration is marking the four-year anniversary of the detention in Russia of American businessman Paul Whelan, whose continued imprisonment is one of several major irritants in tattered relations between Washington and Moscow.

Secretary of State Antony Blinken said in a statement Wednesday that securing Whelan’s release remains a top administration priority.

U.S. officials had hoped to include Whelan in a prisoner swap earlier this month in which they traded detained WNBA star Brittney Griner for a convicted Russian arms dealer, Viktor Bout. The administration considers Whelan, like Griner, to have been wrongfully detained.

Blinken said Whelan and his family are “suffering through an unfathomable ordeal” and he again condemned the American’s conviction, which was based on secret evidence, and 16-year prison sentence.

“His detention remains unacceptable, and we continue to press for his immediate release at every opportunity,” Blinken said. “Our efforts to secure Paul’s release will not cease until he is back home with his family where he belongs.”

Whelan, a Michigan corporate security executive, is jailed in Russia on espionage charges that his family and the U.S. government have said are baseless. U.S. officials said Russia refused to consider including Whelan in the Griner deal, calling it a “one or none” decision.

“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 President Joe Biden’s national security adviser, Jake Sullivan.

The Whelan family supported the exchange that freed Griner, but expressed fears that Whelan would not be released for years.

His brother, David Whelan, said when the swap was announced, “I think we all realize that the math is not going to work out for Paul to come home anytime soon, unless the U.S. government is able to find concessions.”

Paul Whelan, 52, was sentenced in 2020.

In a statement Wednesday, David Whelan said, “Today is the 1,461st day that Paul has been held hostage by the Russian Federation. Russian authorities entrapped him four years ago today. How do you mark such an awful milestone when there is no resolution in sight?”

The anniversary, he said “is both awful and mundane, just another day that Paul has to suffer in a Russian labor colony for being in the wrong place at the wrong time.”