Ukraine’s Ministry of Defence alleges pro-Russian forces have shot down two Ukrainian fighter jets.
The incident reportedly occurred near the village of Dmytrivka on the border with Russia.
A video has been released, purporting to show the wreckage.
Anti-aircraft missiles were fired at four jets carrying out an exercise in the area, according to a statement from the defence ministry.
An adviser to the Ukrainian Interior Ministry, Anton Gerashchenko also accused Moscow of arming the rebels: “The Ukrainian Interior Ministry has received indisputable evidence proving the involvement of [Sergei] Shoigu, the Russian Defence Minister, being actively involved in handing over weaponry, ‘GRAD’ rocket launchers, tanks and artillery to terrorists from the Donetsk People’s Republic and Luhansk People’s Republic.”
Nothing is known about the planes’ pilots.
Meanwhile fighting has resumed between the Ukrainian army and separatists in the rebel-held region of Donetsk in the east of the country.
Residents are said to be preparing to flee their homes.