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 mounts from sustained artillery strikes and rebel cities slip into a humanitarian disaster. At least 52 deaths were reported Wednesday, along with 64 wounded; with the dangers of the war zone blocking any reports from Luhansk, the actual casualty figures could be 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 outskirts has become more intense.
Luhansk city authorities reported running battles between the two sides. By early evening, government forces took control of ‘‘significant parts’’ of the city, just 12 miles from the Russian border, said Andriy Lysenko, a spokesman for Ukraine’s National Security Council.
A Ukrainian SU-25 plane was shot down near Luhansk, Lysenko told TV station 112 late Wednesday. He said the pilot’s location was unknown.
Hard-hit Luhansk has been without electricity, running water, or phone connections for 18 days due to the fighting. Russia has sent a massive aid convoy to help residents there but it is still stuck at the border, not yet approved by Kiev because its proposed route lies through rebel-held territory.
Ukraine has accused Russia of arming and supporting the separatists, a charge Russia denies. Ukraine and the West fear the convoy — with more than 200 trucks — could assist the separatist militia.
Donetsk, meanwhile, has come under daily shelling attacks from all sides. On Wednesday morning, rockets slammed into residential areas, including the Donetsk suburb of Makiivka. More rockets hit in the afternoon.
‘‘I was with my grandmother in the bathroom, because there is a bearing wall in there,’’ said Anna Zyukova, 22. ‘‘And then all of sudden, bam-bam.’’
Residents in Makiivka huddled in groups near a basement shelter Wednesday, chatting and listening as rockets flew in and out several miles away.
At a rebel camp closer to the fighting, a rebel commander who identified himself only as ‘‘Chaika’’ — Russian for seagull — said he was at a loss to explain why army shells were hitting apartments. ‘‘We purposely don’t take up positions where people live,’’ he said — a statement Ukrainian officials have repeatedly dismissed.
As the government sought to retake a major railroad and a highway that leads to Russia, nine troops were killed and 22 wounded overnight in Ilovaysk, a town east of Donetsk, said Lysenko, the Kiev spokesman.
Among those killed in Ilovaysk was a Ukrainian-American known by the nom de guerre of ‘‘Franko,’’ said Anton Herashchenko, an adviser to the interior minister. He said Franko was an American citizen with a military background who had been living in eastern Ukraine for 10 years and obtained Ukrainian citizenship before joining the army.
The Kiev government is also pursuing diplomatic efforts to resolve the conflict, which the United Nations says has killed more than 2,000 people and displaced over 340,000 since its start in mid-April.
Ukrainian President Petro Poroshenko will host German Chancellor Angela Merkel this weekend in Kiev before meeting next week with Russian President Vladimir Putin in Minsk, the capital of Belarus.