Brittney Griner, the American basketball superstar, has written to US President Joe Biden pleading for help.
Griner has been detained in Russia for over four months on what Russia says are drug charges.
In the letter, which arrived at the White House on Monday, she wrote about her fear that she might never return to US soil.
Government officials confirmed they received communication from the Phoenix Mercury player.
A spokeswoman from the National Security Council on Monday said President Biden has been clear about the need to see all US nationals who are held hostage or wrongfully detained abroad released, including Brittney Griner.
US authorities also reiterated that they are working “aggressively – using every available means – to bring her home”.