Russia is closing in on Lysychansk. Here's why it matters.

nbcnews.com: Russia appears to have dealt Ukraine a significant setback in the battle for the country’s east, breaking through the defenses around a key city and opening the possibility that Kyiv’s troops in the area could be surrounded.

In recent days, Russian forces have gained ground around Lysychansk, according to Ukrainian officials and Western military analysts, closing in on the city while fighting for full control of its battle-scarred twin, Sievierodonetsk.

The advance puts Russia in sight of capturing or surrounding the last two holdout cities in Luhansk province, which, together with neighboring Donetsk, form the eastern industrial region of the Donbas, which has become the focal point of the war.

This phase of the conflict has been marked by brutal artillery exchanges, with Kyiv urging the U.S. and its Western allies to send more of the heavy firepower it needs to counter Moscow’s forces.

TOPSHOT-UKRAINE-RUSSIA-CONFLICT (Aris Messinis / AFP via Getty Images)

The Ukrainian army said Tuesday that Russian troops had captured a number of key villages south of Lysychansk, allowing them to bombard the city, which has already been heavily shelled for weeks, from closer range and raising fears that they could try to encircle Ukrainian forces from that direction.

The development is a “clear setback” for Ukraine, the Institute for the Study of War, a U.S.-based military think tank, said in its daily assessment Tuesday.

Ukrainian and Russian forces have been waging a street-to-street battle for weeks over control of Sievierodonetsk, which lies on the other side of the Siverskyi Donets River. The city’s defenders have been confined to its industrial zone, but they have continued to hold out, Luhansk Gov. Serhiy Haidai said Wednesday.

It was believed that Russia might have to wait to take full control of Sievierodonetsk and then attempt a risky river crossing — which it has struggled with before — before it could threaten Lysychansk from the northeast. But now it appears to be closing in from the southwest.

Russian forces “may be able to threaten Lysychansk in the coming days while avoiding a difficult opposed crossing of the Siverskyi Donets River,” the Institute for the Study of War said.

The Kremlin’s forces have achieved a “tactical breakthrough” near Lysychansk, said the head of intelligence at the consultancy Le Beck, Michael A. Horowitz, a geopolitical and security analyst.

“The Russian army has breached through some of the Ukrainian defenses and are now approaching Lysychansk,” he said. “Although they are staging a staunch and brave defense of the area, the Ukrainian military may have to make some difficult choices in the coming days or weeks.”

Oleksiy Arestovych, an adviser to President Volodymyr Zelenskyy, was quoted by the Ukrainian news agency Unian on Tuesday as saying the Ukrainian armed forces were having “big problems” near Sievierodonetsk and Lysychansk. He said the threat that the Russians will try to encircle Ukrainians in the area is “absolutely real.”

Taking the twin cities would give Moscow full control of Luhansk province, moving it closer to achieving its objective of capturing the entire region.

The gains will come as a boost for Russian President Vladimir Putin, who made capturing the Donbas his primary objective after military setbacks early in the war forced Moscow’s troops to retreat from around Kyiv, the capital. Putin laid flowers Wednesday in memory of the war dead as both countries marked the anniversary of Nazi Germany’s invasion of the then-Soviet Union in 1941, which Ukrainian officials have compared to Moscow’s invasion of their country just short of four months ago.

Russians “control about 97% of the Luhansk oblast,” said defense analyst Konrad Muzyka, the director of Rochan Consulting, based in Poland, which specializes in Russia and Belarus. “Once they capture Sievierodonetsk fully and then Lysychansk, they will be on the verge of fulfilling one of the goals of the second phase of this military operation. It is incredibly important for Russia that this happens from their point of view.”

UKRAINE-RUSSIA-CONFLICT (Anatolii Stepanov / AFP via Getty Images)

While it would be a “significant blow” to the Ukrainian army, the breakthrough near Lysychansk is not itself a major turning point in the war, Horowitz said, as the Russian forces are still grinding through Ukrainian defenses rather than making swift breaches.

“We’re in a long war, where battles just aren’t as decisive as they used to be,” he said.

The next few days will be critical, Muzyka said, and if the Russian forces continue to capture settlements west of Lysychansk, it could indicate that their aim is to encircle the city and cut off potential withdrawal routes for Ukrainian troops. That could mean more urban warfare like what was seen for weeks in the streets of Sievierodonetsk, as Ukrainians are likely to dig in.

Ultimately, if this week’s breakthrough does bring about the full capture of the Luhansk oblast, it would leave Russia in control of a large chunk of the Donbas, and Moscow would be likely to immediately sharpen its focus on the other half of the key eastern region.

“If Russians are successful in this area, we are probably looking at a relatively fast approach of Russian forces to Slovyansk,” a strategic city in the nearby Donetsk region, Muzyka said.

“And then we are looking at the start of the battle for Donetsk.”