Brittney Griner urges fans to write American detainee Paul Whelan

Two weeks after she was released from a Russian penal colony, Brittney Griner has urged supporters to write to Paul Whelan, an American detained in Russia.

In a letter posted to Instagram, the US basketball star thanked fans, saying their notes to her in custody "helped me not to lose hope".

Griner had been detained on drug charges for nearly 10 months, before returning home in a prisoner swap.

Mr Whelan, sentenced to 16 years on espionage charges, was left behind.

"There remain too many families with loved ones wrongfully detained," Griner wrote. "I hope you will join me in writing to Paul Whelan and continuing to advocate for other Americans to be rescued and returned to their families."

Paul Whelan's brother David Whelan told the BBC his family was grateful for Griner's support.

"Someone who has been through what she has doesn't have to be as thoughtful and kind as she has been," he said.

Griner, 32, an All-Star centre with the WNBA's Phoenix Mercury and a two-time Olympic gold medallist, was first arrested in Russia in February - days before Russia invaded Ukraine - after authorities at a Moscow airport found cannabis oil in her luggage. She was later convicted of smuggling and possessing narcotics and sentenced to nine years in a penal colony.

Griner's case drew international attention, with high-profile figures like former Secretary of State Hillary Clinton and NBA star Lebron James calling on the White House to secure her release.

But the basketball star's plight also put a spotlight on another American detainee in Russia - Mr Whelan - a corporate security executive who's been jailed for nearly four years. He is serving a 16-year prison sentence on espionage charges that the American government has said are fabricated.

And to some, Griner's release was made bittersweet by the White House's failure to secure Mr Whelan's freedom as well.

Russia traded Ms Griner for arms dealer Viktor Bout, convicted in 2011 of conspiring to kill Americans, but the Kremlin was reportedly unwilling to include Mr Whelan in the deal.

"The choice was one or none," Secretary of State Antony Blinken said at the time of Griner's release.

Last week, Griner said she planned to return to the basketball court next year, joining her WNBA team in Phoenix for their upcoming season.