Ukrainian units stormed through Russian defensive lines, capturing scores of soldiers and villages, as they quickly advanced some ten kilometres into enemy territory.
Overall, the Russian military claims have killed nearly 1,000 Ukrainian troops and destroyed more than 100 armored vehicles since the incursion began on Tuesday.
Moscow on Saturday launched a "counter-terror operation" in three border regions adjoining Ukraine to halt Kiev's biggest cross-border offensive in the two-and-a-half year conflict.
The Kremlin declared a “federal-level” emergency in the Kursk region following the large-scale incursion and sent reinforcements there on Friday.