Ukrainian troops say they have made a significant push into rebel-held territory, claiming control over a large part of the separatist stronghold of Luhansk and nearly encircling Donetsk, the largest city still in rebel hands.
The push follows days of street battles and weeks of shelling.
The army's advance 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 on Wednesday, along with 64 wounded. Due to 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 neighbourhoods in Donetsk have been hit with sustained artillery fire and fighting on the city's outskirts has become more intense.
In the Donetsk region, 43 locals were killed and 42 wounded in less than two days, including in two deadly artillery attacks on Wednesday afternoon in the capital, Donetsk city, local authorities said.
In addition, nine troops died and 22 were wounded in fighting in a town outside Donetsk.
Luhansk city authorities, meanwhile, reported running battles between the two sides.
By early evening, government forces took control of "significant parts" of Luhansk, an eastern city just 20km from the Russian border, said Andriy Lysenko, a spokesman for Ukraine's National Security Council.
The renewed offensive comes as Ukrainian President Petro Poroshenko gears up for a meeting in Minsk with Russia's Vladimir Putin, the heads of Belarus and Kazakhstan, and EU officials next week.
That encounter will come after German Chancellor Angela Merkel jets in to Kiev on Saturday in a show of support for the country's pro-Western leadership.
Poroshenko this week said the army was regrouping to continue its push on the separatist hubs of Donetsk and Luhansk and to fragment the rebel-held territory to stop the flow of weapons from Russia.
Plane shot down
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 massive aid convoy, more than 200 trucks, will be used in some way to help the separatist armed groups.
Also on Wednesday, a Ukrainian warplane was blown out of the sky over rebel-held territory.
Military spokesman Andriy Lysenko said a Su-25 jet was shot close to Luhansk.
Lysenko said it was too early to tell who had shot down the plane, the latest in a string of military jets to be hit, or what had happened to the pilot.