Russia's defence ministry said on Thursday it had taken out military infrastructure at Ukraine's air bases and "suppressed" its air defences, Russian news agencies reported.
The ministry denied reports that its aircraft had been downed over Ukraine.
Earlier, Ukraine's military had said five Russian planes and one helicopter were shot down over its Luhansk region.
"The air defence assets of the Ukrainian armed forces have been suppressed," Interfax news agency quoted the ministry as saying.
"The military infrastructure of the Ukrainian Armed Forces' air bases has been taken out of action.
"Information in foreign media about a Russian plane allegedly being shot down is not true."
164 confirmed dead after two major earthquakes strike Venezuela
Europeans told to protect themselves as deadly heatwave takes its toll
Trump asks Congress for more funds to fight Iran, defying rebuke on war powers
Magnitude 6.9 quake strikes Japan's northeast, no tsunami warning
US, Iran at odds on nuclear inspections, frozen assets in deal to end war
