Russian forces captured two villages in eastern Ukraine and are vying for control of a key highway that could cut supply lines and encircle some frontline Ukrainian forces.
Britain's defence ministry said that Ukrainian forces had withdrawn from some areas near the city of Lysychansk, to avoid being encircled as Russia concentrate reinforcements and firepower in the area.
Ukraine's General Staff said Russian forces took control of the villages of Loskutivka and Rai-Oleksandrivka, and were trying to capture Syrotyne outside Sievierodonetsk, the administrative centre of the Luhansk region.
The governor of Luhansk, Serhiy Haidai, said Putin's forces were "burning everything out in a bid to encircle" Ukrainian troops.
“The Russians are advancing without trying to spare the ammunition or troops, and they aren’t running out of either."
For weeks, Russian forces have pummeled Sievierodonetsk with artillery and air raids, fighting the Ukrainian army house-to-house.
Ukrainian forces remain holed up at the Azot chemical plant on the city’s edge, where about 500 civilians were also sheltering.
Haidai said the Ukrainian soldiers were using the plant's sprawling underground structures, but noted that “the shelling has intensified and even concrete shelters can’t withstand the bombardment.”
"The Russians are using their entire arsenal — heavy artillery, tanks, aircraft.”
He said Russian forces were also pressing their offensive on Lysychansk, which is located on a steep river bank facing Sievierodonetsk.
Haidai said that Lysychansk was also facing a relentless Russian artillery barrage, concentrating over 100 multiple rocket launchers to “pummel entire blocks,” killing at least one civilian and wounded three others in the last 24 hours.
The Russian military currently controls about 95% of the Luhansk region and about half of the neighbouring Donetsk region of Donbas.
Asked about prospects for a political settlement, Kremlin spokesman Dmitry Peskov told reporters on Thursday (local time) that “it's possible after Ukraine meets all the Russian demands.”
The Kremlin has previously demanded that Ukraine accept Russia's sovereignty over the Crimean Peninsula, which Moscow annexed in 2014, and acknowledge the independence of the separatist regions in the east.
Moscow also has noted that Ukraine should recognise the situation on the ground, a reference to other land gains that Russia has made in Ukraine's south where it captured the Kherson region and part of the Zaporizhzhia region.