The Russian side has assured U.S. Secretary of State John Kerry that it has no fears about the health of Ukrainian pilot Nadia Savchenko, Russian Foreign Minister Sergei Lavrov has said.

"We have only confirmed that the condition of Nadia Savchenko's health, on which many have been trying to speculate, does not cause any fears; she remains under constant medical surveillance of Russian doctors," the Russian minister told reporters on Friday.

Lavrov confirmed that Kerry did raise the question of the Nadia Savchenko case at his meeting with Russian President Vladimir Putin. "He was given an answer known to everyone: representatives of the Foreign Ministry and the Kremlin press service have spoken about that. I have nothing to add," the foreign minister said.

A Russian court sentenced Savchenko to 22 years in custody on March 22. The sentence has yet to take effect, but Savchenko has prohibited her lawyers from challenging it.