Ukrainian servicewoman Nadia Savchenko, who has been given a 22-year sentence in Russia, is unlikely to be able to return to Ukraine within a month, her lawyer Mark Feygin has said.

"Most probably, Savchenko will not be released either before Easter or by the end of May. Don't listen to gossipers," Feygin wrote on Twitter on Monday.

He said he was visiting the detention facility where Savchenko is being held.

Feygin wrote on Twitter earlier that the return of his client to Ukraine might take a while.

Ukrainian President Petro Poroshenko said he had agreed on the preliminary timeframe of Savchenko's transfer to Ukraine in his telephone conversation with Russian President Vladimir Putin.

The Donetsk City Court in Russia's Rostov region found Ukrainian servicewoman Nadia Savchenko guilty of conspiracy to murder Russian journalists Igor Kornelyuk and Anton Voloshin for reasons of hatred and sentenced her to 22 years in a general penitentiary on March 22. The court also convicted her of attempted murder and illegal crossing of the Russian border.

The sentence took effect on April 5.