A column of 32 tanks has crossed into Ukraine from Russia as a ceasefire between Kiev and pro-Russian separatists becomes closer to collapse.
In a televised briefing, military spokesman Andriy Lysenko said that a convoy of 32 tanks, 16 howitzer cannons and 30 trucks of troops and equipment had crossed into the rebel-held area of Luhansk.
"The deployment continues of military equipment and Russian mercenaries to the front lines," he said.
The move by Russia comes just a day after five Ukrainian soldiers were killed in fighting with rebels in the country's restive eastern regions.
Ukraine's military spokesman Andriy Lysenko said: "Over the past day we lost five Ukrainian soldiers and 16 were wounded."
Rebels in eastern Ukraine have claimed that President Petro Poroshenko has broken the peace agreement signed between Kiev and the separatists in September by proposing to cancel autonomy for the eastern regions of Luhansk and Donetsk.
Poroshenko had this week stated that the rebel elections had jeopardised "the entire peace process" following a conflict which has taken the lives of more than 4,000 people since April.
The European Organisation for Security and Co-operation in Europe (OSCE) has warned that the "bloodletting" in the country is continuing despite the ceasefire with many incidents of shelling, including one which killed two children in Donetsk.