American basketball star Brittney Griner has pleaded guilty to drug possession charges on the second day of her trial in a Russian court in a case that could see her sentenced to up to 10 years in prison.

The abrupt guilty plea by the Phoenix Mercury star and two-time Olympic gold medallist came amid a growing chorus of calls for Washington to do more to secure her freedom nearly five months after her arrest, amid rising tensions between the United States and Russia over Ukraine.

A senior Russian diplomat said earlier that no action could be taken by Moscow on Griner’s case until the trial was over, and her guilty plea could be an effort by her and her advisers to expedite the court proceedings.

Brittney Griner is escorted to a courtroom
Brittney Griner was escorted to the courtroom in handcuffs (Alexander Zemlianichenko/AP)

Griner, 31, was detained at Moscow’s Sheremetyevo Airport while returning to play basketball in Russia, and police said they found vape canisters containing cannabis oil in her luggage.

Speaking through an interpreter, Griner told the court that she had no intention of committing a crime and had acted unintentionally because she had packed for Moscow in a hurry. The trial was then adjourned until July 14.

Griner emphasised “that she had committed this act through negligence, unintentionally”, her lawyer, Maria Blagovolina, told reporters outside the court near Moscow after the guilty plea.

“We of course hope for the leniency of the court,” Ms Blagovolina said.

Brittney Griner is escorted to a courtroom
The athlete has been designated by the US as wrongfully detained (Alexander Zemlianichenko/AP)

“Considering all the circumstances of the case, taking into account the personality of our client, we believe that the admission of guilt should certainly be taken into account.”

She added that other defence witnesses would be questioned at a later session.

Griner’s other lawyer, Alexander Boikov, said she admitted that the canister “was hers, but she said that it was unintentionally brought to Russia, because she was in a hurry as she was packing and it was just by accident it ended up in her luggage”.

The athlete was escorted to the courtroom in handcuffs and was wearing a bright red T-shirt and tracksuit bottoms. She also held a photo of her wife, Cherelle.

Brittney Griner playing basketball
The trial of the Phoenix Mercury star and two-time Olympic gold medallist began last week (Ralph Freso/AP)

Elizabeth Rood, deputy chief of mission at the US Embassy in Moscow, told reporters after the hearing that she had spoken to Griner in the courtroom and shared with her a letter from US president Joe Biden that she had read.

“She’s eating well, she’s able to read books and under the circumstances she’s doing well,” Ms Rood said of Griner.

“I would like again to emphasise the commitment of the US government at the very highest level to bring home safely Ms Griner and all US citizens wrongfully detained, as well as the commitment of the US Embassy in Moscow to care for and protect the interests of all US citizens detained or imprisoned in Russia,” she added.

Russian deputy foreign minister Sergei Ryabkov bristled at the US description of Griner as “wrongfully detained” and warned that “attempts by the American side to make noise in public … don’t help the practical settlement of issues”.