Nadezhda Savchenko was fighting with a Ukrainian volunteer brigade against Russian-backed rebels in eastern Ukraine when she was captured in June 2014.
Russia says she was a spotter who called in coordinates for a mortar attack that killed two journalists and several civilians. A verdict is expected Monday in her trial on charges of accessory to murder.
A senior Obama administration official has said the US president urged Savchenko's release in a phone call with Putin this week.
The Foreign Ministry later today echoed that position in a statement that followed a meeting between ministry officials and ambassadors from countries of the European Union, which has called for Savchenko's release.
The ministry "pointed out the unacceptability of attempts to place pressure on Russian authorities" in the case, it said.