NEWYou can now listen to Fox News articles!

A major city and the last remaining stronghold in Eastern Ukraine could soon fall to Russian forces, a senior advisor to said.

Lysychansk, in the Eastern province of Luhansk, could fall as Russian forces continue their assault on the city and look to complete their siege of its sister city Sievierodonetsk, according to Zelenskyy adviser Oleksiy Arestovych.

The are separated by the Siverskyi Donets River, with Sievierodonetsk in the north and Lysychansk to the south. Last month, President Zelenskyy said the two cities stood in the way of total Russian control in the region.

LYSYCHANSK, UKRAINE -- JUNE 13, 2022: A view of Severodonetsk, as seen from Lysychansk, Ukraine, Monday June 13, 2022. (Marcus Yam / Los Angeles Times via Getty Images)

LYSYCHANSK, UKRAINE — JUNE 13, 2022: A view of Severodonetsk, as seen from Lysychansk, Ukraine, Monday June 13, 2022. (Marcus Yam / Los Angeles Times via Getty Images)

While Russian forces have been attacking both cities in recent weeks, their occupation of Sievierodonetsk provides them a new strategic advantage as these forces were seen crossing the river and entering Lysychansk from the north, the adviser said.

“This is indeed a threat [and] I do not rule out any one of a number of outcomes here,” Arestovych said, according to Reuters. “Things will become much more clear within a day or two.”

A column of smoke rises from an industrial area outside of  Lysychansk, Ukraine, Monday June 13, 2022. (Marcus Yam / Los Angeles Times via Getty Images)

A column of smoke rises from an industrial area outside of  Lysychansk, Ukraine, Monday June 13, 2022. (Marcus Yam / Los Angeles Times via Getty Images) (Marcus Yam / Los Angeles Times via Getty Images)

The fall of the final holdout for Ukrainian troops in the region will shift the landscape of the war, the adviser cautioned.

“If Lysychansk is taken, strategically it becomes more difficult for the The front lines will be flatter and there will be a frontal attack rather than from the flanks,” Arestovych predicted, per the report.

Conversely, weapons and ammunition from the West could result in Ukraine’s successful defense of the town, he said.

“The more Western weapons come to the front, the more the picture changes in favor of Ukraine,” the advisor added.

Ukrainian President Volodymyr Zelensky visits the front-line positions of Ukrainian military in Donbass, Ukraine on December 06, 2021. (Photo by Ukrainian Presidency / Handout/Anadolu Agency via Getty Images)

Ukrainian President Volodymyr Zelensky visits the front-line positions of Ukrainian military in Donbass, Ukraine on December 06, 2021. (Photo by Ukrainian Presidency / Handout/Anadolu Agency via Getty Images) (Photo by Ukrainian Presidency / Handout/Anadolu Agency via Getty Images)

Russian separatist forces have already claimed control of the city — though they have not “liberated it” — while Ukrainian officials have disputed this claim.  

Last month, President Zelenskyy confirmed that Russian forces occupied 20 percent of Ukraine, including most of which includes Luhansk in the east and Donetsk in the South.

“The Russian army has already destroyed almost the entire Donbas. Once one of the most powerful industrial centers in Europe is simply devastated,” Zelenskyy said on June 2. “The occupiers are destroying it city after city.”

“We still don’t even know exactly how many of our people were killed by the occupiers. At least tens of thousands – tens of thousands in a little less than 100 days,” he added.