Barack Obama urges Vladimir Putin to release Ukrainian pilot Nadezhda Savchenko

US President Barack Obama has urged Russian President Vladimir Putin to release Ukrainian pilot Nadezhda Savchenko from Russian prison.

Savchenko was fighting with a Ukrainian volunteer battalion against Russia-backed rebels in eastern Ukraine when she was captured in June 2014.

Russia claims she was acting as a spotter who called in coordinates for a mortar attack that killed two Russian journalists and several other civilians.

She has gone on a hunger strike and refused to take water after a court hearing last Thursday. Rights advocates fear she could die if she keeps refusing water.