All that remained of a Russian border post was a tableau of destruction: Sheet metal flapped in the wind, customs declarations fluttered about, and stray dogs roamed under a road-spanning sign that said, “Russia.”

Kicking up dust, Ukrainian armored vehicles rumbled past, unimpeded, as the flow of men and weaponry carried on in the biggest foreign incursion into Russia since World War II, an offensive now nearing the end of its first week since the breach of the border here in Sudzha and at several other sites.

At the crossing point, a Ukrainian soldier posted on the roadside waved at the forces passing by, days after Russia’s head of the general staff declared that the attack had been rebuffed.

At the border, the detritus of a losing battle — and signs of soldiers caught by surprise — were scattered about: bullet cartridges tinkled underfoot, discarded body armor lay on the asphalt.

Taking the fight to Russian soil was a weighty moment for Ukraine in its war with Russia, coming two and a half years after Russia launched a full-scale invasion and 10 years after Russia intervened militarily to seize territory and support separatist client states in eastern Ukraine.

Within the first month of the war, Ukraine did strike back with a cross-border helicopter assault and has regularly bombarded Russian oil refineries and airfields with a fleet of homemade drones. Two smaller, earlier forays into Russia by Russian exile groups backed by the Ukrainian Army ended in quick retreats.