"The armoured vehicles have been rolled up from the border with the Russian Federation, under the cover of artillery fire on positions of Ukrainian army forces, with careful use of disguise," the report reads.

"At the same time, the enemy mobile groups in this region, reinforced by the armored vehicles, have been attempting to push back Ukrainian army troops from the Siverskiy Donets River, alternating shelling with ground attacks," Tymchuk wrote.

"The insurgents have been using the tanks (one or two units) mainly as a means of strengthening the firepower of their infantry teams. There is [also] a lot of activity with mortar fire by the Russian-backed insurgents," he added.