“The deployment continues of military equipment and Russian mercenaries to the frontlines,” spokesman Andriy Lysenko said in a televised briefing referring to Thursday’s cross-border incursion.
NATO said it has seen an increase in Russian troops and equipment along the Ukraine border was looking into the reports.
“We are aware of the reports of Russian troops and tanks crossing the border between Ukraine and Russia,” a NATO military officer told Reuters.
“If this crossing into Ukraine is confirmed it would be further evidence of Russia’s aggression and direct involvement in destabilising Ukraine.”
The report of a new Russian movement of armour across the border follows a charge on Thursday by pro-Russian rebels in eastern Ukraine that Kiev government forces had launched a new offensive - which Kiev immediately denied.
Sporadic violence has continued since a 5 September truce in a conflict that has cost more than 4,000 lives.
But the ceasefire has looked particularly fragile this week, with separatists and the central government accusing each other of violations after separatist leaders held elections in self-proclaimed “people’s republics” last Sunday.
“Supplies of military equipment and enemy fighters from the Russian Federation are continuing,” Lysenko said.
He added that five Ukrainian soldiers had been killed and 16 wounded in the past 24 hours despite the ceasefire.
Fifteen civilians were wounded by shrapnel in Donetsk, the mayor’s office said, in a night of shelling in two neighbourhoods near the ruins of the airport, where government troops are holding out.
Some 150 mourners later attended an emotional memorial service in the city for two teenage boys killed when a shell hit a school playing field on Wednesday.
Kiev and the insurgents blamed each other for the incident.
Claims of fresh troop movements are reinforcing fears of a return to all-out fighting.
The Ukrainian president, Petro Poroshenko, said this week that the rushed elections in the Donetsk and Luhansk regions, which the Kiev government and EU had declared illegal, had violated the September peace accord.
He said the votes - which the rebel leaders claimed gave them a mandate to negotiate directly with Kiev - had “torpedoed” an offer of autonomy for the east and ordered troops to reinforce frontline cities.
A Kremlin adviser said on Friday that Russia was committed to the two-month-old agreement and wanted further talks held to build on peace moves involving government forces and separatists.
Foreign policy adviser Yuri Ushakov also said Russia respected the will of voters after the separatist elections, but following western criticism of Moscow’s stance on Sunday’s vote, he said he had deliberately chosen the word “respect” rather than “recognise”.
The financial isolation over the Ukraine crisis - along with falling oil prices - has hammered Russia’s flagging economy, with the rouble plunging early on Friday to a new record low against the euro.
Source: The Guardian