U.S. State Department spokesman Jen Psaki says the life of Ukrainian Air Force officer Nadia Savchenko "hangs in the balance" after 54 days on a hunger strike in a Russian prison.
Psaki called Savchenko "a hostage to Russian authorities" and said Washington demanded her immediate release in accordance with the commitments Russia made under an agreement signed in Minsk in September.
A court in Moscow announced on February 4 that it would issue a ruling on February 10 about whether to grant a request by Russia's Investigative Committee to extend Savchenko's pretrial detention until May 13.
Savchenko began her hunger strike on December 13 protest her incarceration by Russian authorities.
She was transferred to the hospital ward at Moscow's notorious Matrosskaya Tishina detention center on January 29 because of what medical personnel described as "abrupt weight loss."
Savchenko was captured by pro-Russian separatists in eastern Ukraine in June and transferred to Russian custody in July.
Russian prosecutors have charged her with involvement in the deaths of two Russian journalists who were killed while covering the war in eastern Ukraine.