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."
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