KOZACHA LOPAN, Ukraine: There are still bodies on the battlefield, lying where they fell on farm fields or inside burned-out tanks as Ukrainian troops swept through Russian-occupied territory in a major counteroffensive this month.

In this northeastern corner of Ukraine, the Russian army was pushed all the way back across the border into Russia after holding the area for months. But artillery shells still whistle through the air, fired from inside Russia and landing with resonating thumps and billows of black smoke on Ukrainian territory.