Savchenko, 34, is demanding she be repatriated to Ukraine after a judge in the southern Russian town of Donetsk yesterday unexpectedly postponed her final address to court as her trial over the 2014 killing of two Russian journalists in east Ukraine nears an end.
Savchenko's defence lawyers visited her today at her detention centre in southern Russia but failed to persuade her to stop the hunger strike.
"Our arguments did not work," lawyer Nikolai Polozov told AFP. "Her only demand is that she be immediately returned to Ukraine."
He said she had not been drinking water since the trial was adjourned.
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Her supporters are concerned that by refusing to drink water she may damage her health irreparably or not live long enough to attend the next hearing set for Wednesday.
Refusing both food and water is known in Russia as a "dry hunger strike" and was a method of last resort for some Soviet dissidents under Communism.
Savchenko has fasted before to protest the accusations against her but has never before refused both food and water.
Polozov said her defence team would not be able to visit her this weekend and during subsequent public holidays on Monday and Tuesday in Russia.
If she is not in court on Wednesday, her lawyers would start looking for her in local hospitals, Polozov said.