DONETSK, Ukraine – After days of street battles and weeks of shelling, Ukrainian troops made a significant push Wednesday into rebel-held territory, claiming control over a large part of the separatist stronghold of Luhansk and nearly encircling Donetsk, the largest rebel-held city.

The advance of the Ukrainian army against pro-Russian separatists comes as the civilian death toll is mounting from sustained artillery strikes and rebel cities are slipping into a humanitarian disaster. At least 52 deaths were reported Wednesday, along with 64 wounded – and because of the dangers of the war zone in eastern Ukraine, no deaths were reported from Luhansk, meaning the actual toll could be even higher.

Ukrainian troops have been trying for weeks to drive the rebels out of Luhansk and cut off Donetsk, a city of 1 million that has shrunk by a third as frightened residents fled. In the last few days, several neighborhoods in Donetsk have been hit with sustained artillery fire and fighting on the city’s outskirts has become more intense.

The death toll mounted quickly on Wednesday. In the Donetsk region, 43 locals were killed and 42 wounded in less than two days,local authorities said. In addition, nine troops died and 22 were wounded in fighting in a town outside Donetsk.