Russian forces have advanced toward the outskirts of Slovyansk within eastern Ukraine’s so-called “fortress belt” of heavily fortified cities in the Donetsk region, Chief of the General Staff Valery Gerasimov said Thursday.

Speaking at an undisclosed location while inspecting troops from Russia’s “South” grouping of forces, Gerasimov said that Russian troops are positioned just 4 kilometers (2.5 miles) from the eastern outskirts of Slovyansk.

The general noted that Russian forces captured at least three villages to the northeast and southeast of the city over the summer, with active street fighting continuing in two other settlements.

Gerasimov added that Russian operations are currently advancing along a 160-kilometer (99-mile) front.

The Washington-based Institute for the Study of War (ISW) said earlier this week that Russian troops have intensified efforts to push toward Slovyansk from the east and southeast following unsuccessful assault attempts from the northeast.