The athlete was detained in February after cannabis oil was allegedly found in her airport luggage.
Brittney Griner has pleaded guilty to drug possession and smuggling during her trial in Moscow but said she had no intention of committing a crime
The jailed American basketball star said she had acted unintentionally because she was packing in haste, according to court reports.
Griner was detained in February at Moscow’s Sheremetyevo Airport after vape canisters with cannabis oil were allegedly found in her luggage.
She faces up to 10 years in prison if convicted of large-scale transportation of drugs.
The trial of the two-time Olympic gold medalist began last week amid growing calls for Washington to secure her freedom, nearly five months after her arrest.
Russian Deputy Foreign Minister Sergei Ryabkov warned on Thursday that “attempts by the American side to make noise in public ... don’t help the practical settlement of issues.”
The White House said US President Joe Biden had called Griner’s wife on Wednesday to assure her that he’s doing all he can to obtain the athlete’s release, as soon as possible.
They spoke after Biden read a letter from Griner in which she said she feared she’d never return home.
The United States may have little leverage with Moscow because of heightened tensions due to Russia’s war in Ukraine.
The US State Department has designated Griner as "wrongfully detained" and has passed her case to its special presidential envoy for hostage affairs.
Ryabkov has also played down any suggestions that the basketball player could be immediately returned in a prisoner swap until her trial is over.
“This is a serious offence, confirmed by indisputable evidence ... Attempts to present the case as if the American was detained illegally do not hold up,” Foreign Ministry spokesman Alexei Zaitsev said Wednesday.
“The law has been violated, and arguments about the innocent nature of Griner’s addiction, which, by the way, is punishable in some U.S. states, are inappropriate in this case."