The European Union's foreign policy chief Federica Mogherini urged Moscow on Wednesday to "immediately and unconditionally" release a Ukrainian pilot who has gone on hunger strike to protest her detention and trial in Russia.

"This is no longer just a judicial or political case: now it's a matter of human compassion," Mogherini said in a statement, adding that the woman's release would be in line with Russia commitments under the Minsk peace accords aimed at ending the conflict in Ukraine, and which require the release of all hostages and prisoners.