Russia's military has said it is "continuing to repel" a Ukrainian cross-border incursion into the western Kursk region - a surprise attack now in its fourth day.
The Russian defence ministry said Ukraine lost more than 280 military personnel in the past 24 hours - a claim that has not been independently verified.
Reports suggest that Ukrainian troops are operating more than 10km (six miles) inside Russia - the deepest cross-border advance by Kyiv since Moscow launched a full-scale invasion in February 2022.
Ukraine has not openly admitted the incursion, but President Volodymyr Zelensky said on Thursday that Moscow must "feel" the consequences for its invasion.
Separately, Ukraine's military said it hit overnight a military airfield deep inside Russia, destroying warehouses with guided bombs.
In a statement, the Ukrainian military reported a huge blaze and multiple detonations at the Lipetsk airfield, more than 350km (217 miles) from Ukraine's border, after the overnight strike.
Lipetsk's regional authorities said a state of emergency was now in place in the area, confirming the detonations at an "energy infrastructure facility". Residents of four nearby villages were being evacuated.
In a statement on Tuesday, the Russian defence ministry said its forces were repelling "an attempt by the Ukrainian armed forces to invade the territory of the Russian Federation".
It said Russia was using aviation and artillery, managing to suppress "raid attempts by enemy units".
Earlier on Tuesday, a "federal state of emergency" was declared in the Kursk region - a move that underlines how grave the current situation is.
Russia said that up to 1,000 Ukrainian troops, supported by tanks and armoured vehicles, entered the Kursk region on Tuesday morning.
"Russia brought the war to our land and should feel what it has done,” Mr Zelensky said in a video address late on Thursday.
"Ukrainians know how to achieve their goals. And we did not choose to achieve our goals in the war," he added.
