Thursday, Russian soldiers bombarded an eastern Ukrainian city, and both sides engaged in fierce street fighting, which Ukrainian President Volodymyr Zelenskyy claimed might determine the fate of the vital Donbas area.

In the wake of a series of setbacks in the 3-month-old war, Russia focused its eyes on the industrial Donbas region of coal mines and factories, where Moscow-backed separatists had been fighting Ukrainian troops for years and already held large swaths of land before the invasion.

But, as elsewhere, the Russian advance has been slower than anticipated, and the war for control of Sievierodonetsk has degraded into street-to-street combat, which has been uncommon throughout the campaign.

The governor of Luhansk, Serhiy Haidai, told the Associated Press: "Street battles are occurring with varying degrees of success in city blocks, and fierce fighting continues in the city itself." The Ukrainian military is fighting for every street and home.

Sievierodonetsk, which became the administrative capital of the Luhansk region after the previous one was captured by rebels in 2014, is the region's final unclaimed territory.

Zelenskyy referred to the arduous war for Sievierodonetsk as the "epicenter" of the more significant Donbas conflict, including Luhansk and Donetsk.

"In many ways, the fate of our Donbas is being decided there," Zelenskyy said in his nightly video address, which was shot outside his Kyiv office on Wednesday.

Analysts believe Russia's steady advance in the Donbas could eventually pave the way for a diplomatic end to the conflict.