A massive prisoner swap involving the United States and Russia was underway Thursday, a person familiar with the matter said.

The person, who spoke on the condition of anonymity because details had not been publicly disclosed, did not specify who is included in the deal. But Americans considered by the U.S. to be wrongfully detained in Russia include Wall Street Journal reporter Evan Gershkovich and Paul Whelan, a corporate security executive from Michigan. Both had been convicted of espionage charges that the U.S. government considered baseless.

Russia has long been interested in getting back Vadim Krasikov, who was convicted in Germany in 2021 of killing a former Chechen rebel in a Berlin park two years earlier, apparently on the orders of Moscow’s security services.

Speculation had mounted for weeks that a swap was near because of a confluence of unusual developments, including a startingly quick trial and conviction for Gershkovich that Washington regarded as a sham. He was sentenced to 16 years in a maximum-security prison.

Also in recent days, several other figures imprisoned in Russia for speaking out against the war in Ukraine or over their work with the late Russian opposition leader Alexei Navalny were moved from prison to unknown locations.