Ukraine's Internal Affairs Minister Arseny Avakov said that three tanks had crossed the Russian border along with armoured personnel carriers into the Luhansk region in the east, before moving into the neighbouring Donetsk region, BBC reported.
Of the three tanks, one headed out towards the town of Horlivka but was attacked by security forces, Avakov said.
Videos of the tanks entering into Ukraine were uploaded on video-sharing channel, YouTube.
Russia has denied sending the tanks into Ukrainian territory, saying it was "another fake piece of information".
Meanwhile, a vehicle belonging to a separatist leader was blown up in Donetsk late Thursday.
The attack injured four pro-Russian militants.