Ukrainian military aviator Nadia Savchenko, whom Russia has sentenced to 22 years in prison for involvement in the killing of Russian journalists in Donbas, believes a decision on her extradition to Ukraine will be made not earlier than May 23, Savchenko's defense lawyer Mark Feygin said.

"Certainly, she is airing her concerns and her discontent with the fact that the process is being dragged out, although she understands that everything will happen only after the sentence handed down to [Russian citizens Alexander] Alexandrov and [Yevgeny] Yerofeyev takes legal effect," Feygin said.

The sentence that a Kyiv court earlier handed down to Alexandrov and Yerofeyev will take legal effect on May 23.

Feygin said his colleague Nikolai Polozov and he had visited Savchenko at the detention facility earlier in the day.

"We wished Nadia a happy birthday. Thirty-five years is a significant date and a certain milestone. We also passed greetings to her from all of her supporters," he said.

Nadia Savchenko's mother, Maria Savchenko, has not so far been allowed to see her daughter, he said.

"The mother has still not been admitted, and I don't believe they'll admit her, which certainly upset Nadia very much," Feygin said.

Feygin had said earlier that the detention facility administration had not allowed Nadia Savchenko's mother to see her daughter on Wednesday, when the latter turned 35, as she had earlier reached the limit of meetings with relatives.