A spokesman for Ukraine's Security Council says an Air Force fighter jet has been struck and shot down by a missile fired from a Russian plane.
Ukrainian officials have recently accused Russia's armed forces of being directly implicated in attacks on Ukrainian troops battling an insurgency near the Russian border.
Spokesman Andrei Lysenko said in a televised briefing that the pilot of the Sukhoi-25 jet was forced to bail from his craft after it was shot down Wednesday evening.
Pro-Russia rebels, meanwhile, claimed responsibility Wednesday for strikes on two Sukhoi-25 jets.
The Defense Ministry said the second jet was hit by a portable surface-to-air missile, but that pilot was unscathed and managed to land his plane safely.
Moscow denies it is supporting the separatists or sowing unrest in its neighbor.