The president of the WNBA players' union, Nneka Ogwumike, noted in a separate statement that "it has been 75 days that our friend, teammate, sister, Brittney Griner, has been wrongfully detained in Russia."
"It is time for her to come home," Ogwumike added. "Having learned that the US government has now determined that BG is being wrongfully detained we are hopeful that their efforts will be significant, swift and successful."
It was unclear what prompted the shift in approach to Griner's case, though President Joe Biden's administration had been under pressure from members of Congress and others to make her release a priority.
The US last week secured the release of Marine veteran Trevor Reed as part of a prisoner swap that also resulted in a convicted Russian drug trafficker being freed from prison in the US.
ESPN first reported the classification in Griner's case.
Meanwhile, the WNBA announced Wednesday that it would honour Griner with a floor decal and allow the Mercury to pay her without it counting against the team's cap. The decal will feature Griner's initials, BG, as well as her No. 42.
All 12 teams will have the decal on their home courts starting with the season opener on Saturday night. The Mercury open their season at home that night against the Las Vegas Aces.