Ukrainian forces have admitted that Russia's military have crossed into the eastern industrial region of Dnipropetrovsk and are trying to establish a foothold.
"This is the first attack of such a large scale in Dnipropetrovsk region," Viktor Trehubov, of the Dnipro Operational-Strategic Group of Troops told the BBC, although he made clear their advance had been stopped.
Russia has claimed throughout the summer that it has entered the area, as its forces try to push deeper into Ukrainian territory from the Donetsk region.
In early June, Russian officials said an offensive had begun in Dnipropetrovsk, although the latest Ukrainian reports suggest they have barely breached the regional border.
Any Russian advance into Dnipropetrovsk would be a blow to Ukrainian morale, as a US-led diplomatic bid to bring the war to an end appears to be flagging despite President Donald Trump meeting Russia's Vladimir Putin in Alaska.
