Satellite images, collected and analyzed by the private American company Maxar Technologies, show long Russian military convoys passing through the Ukrainian city of Velykyi Burluk and heading for Kharkov.
These include armored personnel carriers and vehicles with artillery.
Major General Kyrylo Budanov, head of the main intelligence service of the Ukrainian Defense Ministry, said Russian forces were regrouping in eastern Ukraine and planning to advance towards Kharkov.
It is not yet known when Russia plans a new major offensive. But the troops are said to be fast approaching and civilians are being asked to leave the region as soon as possible. After what happened in Mariupol and Butsha, more residents are also heeding those calls.