Brittney Griner's defence team has appealed against her nine-year prison sentence in Russia.

The WNBA star was this month jailed for drug possession and drug smuggling with criminal intent for bringing under a gram of cannabis oil into the country nearly six months ago.

Judge Anna Sotnikova rejected Griner's apology and plea for leniency. Griner said she had made an "honest mistake".

Griner was arrested in Moscow's Sheremetyevo International Airport on February 17 for carrying vape cartridges containing cannabis oil in her luggage. She was returning to Russia, where she has played since 2014 during the WNBA offseason.

The eight-time WNBA All-Star was, her lawyers argued, using cannabis for medicinal purposes to treat chronic pain sustained over the course of her career.

The two-time Olympic champion said she accidentally packed the cartridges and was unaware cannabis oil was outlawed in Russia.

United States president Joe Biden slammed the sentence as "unacceptable" and Griner's lawyer Maria Blagovolina told Reuters on Monday that an appeal had been filed.

The US government and Russia are engaged in prisoner swap negotiations that, if successful, would see Griner released to return home.