Pressing ahead with a new summer offensive, Russian forces have entered the Dnipropetrovsk region of eastern Ukraine for the first time in three years of war — signaling their capacity to keep expanding the fight as cease-fire talks show little signs of progress.

Advancing west from the Donetsk region, the main theater of the ground war today, small squads of Russian soldiers began crossing into neighboring Dnipropetrovsk last weekend, according to three Ukrainian officers fighting in the area. A battlefield map by the Washington-based Institute for the Study of War, based on verified combat footage, now shows that Russian forces have secured a tiny foothold in the area.

Russia is unlikely to try to seize the new region, which it has signaled in the past that it has no intentions of doing. Instead, military analysts and Ukrainian soldiers view the push as both symbolic — aimed at denting Ukrainian morale by breaching a new region — and strategic, designed to bolster its defenses in neighboring areas where it has already dug in.

Still, both goals are likely to further widen the battlefield in a war now grinding through its fourth year. An officer with the call sign “Barbarossa” from Ukraine’s 72nd Brigade, which is currently fighting off Russian assaults into Dnipropetrovsk, said that Russia had accumulated “a lot of forces” in the area, and that he expected them to push deeper into the region.

Like other officers quoted in this article, he asked to be identified by his first name or call sign only, in keeping with military protocol.

Russia’s Defense Ministry first claimed on Sunday that some of its forces had reached the administrative border between Donetsk and Dnipropetrovsk and were “continuing their offensive.” Ukraine’s top military command has so far denied that Russian troops have entered Dnipropetrovsk.