Why is the Wagner group taking an 'operational pause' near Bakhmut?

Ukrainian officials have said the fighting for the besieged eastern city of Bakhmut has escalated again. Kyiv says its troops are holding on even as Russia has increased its attacks on their positions. Several civilians were injured and buildings set on fire after Russian shelling hit the nearby Ukrainian-held town of Kostiantynivka. Ukrainian officials have said they are determined to hold on to the city in what's become the longest and bloodiest battle of Russia's year-long war.