Supporters of Ukrainian pilot and parliament member Nadia Savchenko, who has been jailed in Russia since July, are urging social media users to use Twitter to mark her birthday.
Savchenko turned 34 behind bars on May 11 amid renewed international calls for her to be released.
The U.S. ambassador to Ukraine, Geoffrey Pyatt, used the hashtag #FreeSavchenko on Twitter and posted a picture of a birthday card addressed to the Ukrainian military officer.
Savchenko says she was illegally brought into Russia in July 2014 after being abducted by Russian-backed separatists in eastern Ukraine.
She is charged with complicity in the killing of two Russian journalists who died in the Ukraine conflict, as well as illegal border crossing.
Savchenko denies her guilt and says Russia has no right to detain her.
On May 6, a Moscow court extended her pretrial detention until June 30.