Russian troops have been put on the defense in Luhansk as Ukrainian forces continue to advance, and Kyiv looks to retake occupied territory the Kremlin has held for months. 

"Units are making slow advances on at least two axes east from the line of the Oskil and Siverskyy Donets rivers, where forces had consolidated following their previous advance earlier in the month," the U.K. Ministry of Defense said in its Wednesday intelligence update.

RUSSIA CLAIMS TO SECURE UP TO 98% SUPPORT FOR ANNEXATION IN CONTROVERSIAL REFERENDA: REPORT

Ukrainian servicemen check the site where a body of a Ukrainian soldier was found inside an armored vehicle

Ukrainian servicemen check the site where a body of a Ukrainian soldier was found inside an armored vehicle in an area near the border with Russia, in Kharkiv region, Ukraine, Monday, Sept. 19, 2022. In this operation seven bodies of Ukrainian soldiers were recovered from what was the battlefield in recent months.  (AP Photo/Leo Correa)

Defense officials said Russian troops are now "mounting a more substantive defense than previously" as Ukrainian forces have pushed the front lines out of Kharkiv as they advance on Luhansk.

Luhansk, located in the northern Donbas region, remains a chief priority in Russian President Vladimir Putin’s war effort as he looks to illegally annex several regions across eastern and southern Ukraine.

Russian proxies in Luhansk, Donetsk, Zaporizhzhia and Kherson wrapped up five days of "voting" Tuesday in a referendum that looks to garner support in seizing the four regions. 

Western officials and Kyiv have condemned the referenda as "shams" and warned the results would mimic steps Moscow took in Crimea when it reportedly falsified ballot results in favor of Russia’s political aims in 2014. 

Ukraine referendum

Konstantin Ivashchenko (L), former CEO of the Azovmash plant and appointed pro-Russian mayor of Mariupol, visits a polling station as people vote in a referendum in Mariupol on Sept. 27, 2022.  (Photo by STRINGER/AFP via Getty Images)

PUTIN EXPECTED TO SEIZE PARTS OF UKRAINE AS 'SHAM' REFERENDUMS END TODAY

The Kremlin has warned that it will interpret any attack in the war torn regions as an attack on Russia should the referenda "results" show support in joining the Russian Federation. 

Early tallying results released by Russian news outlets Tuesday allegedly showed that as many as 98% of "voters" support Russia’s illegal annexation of Ukraine’s territory. 

However, Ukrainian President Volodymyr Zelenskyy has said he will not recognize the "farce" and that his troops will not stop until they have liberated all of Ukraine from Russian forces, including Crimea. 

"Annexation is the kind of move that pits him alone against the whole of humanity," Zelenskyy said in reference to Putin.

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Ukraine soldiers in Izyum

Ukrainian soldiers sit on infantry fighting vehicles as they drive near Izyum, eastern Ukraine on Sept. 16, 2022, amid the Russian invasion of Ukraine. (JUAN BARRETO/AFP via Getty Images)

"Russia's recognition of these sham referenda as allegedly normal, implementation of the so-called ‘Crimean scenario’ [are] another attempt to annex the territory of Ukraine," he said.

Zelenskyy called for "a clear signal" from the international community to show that Russia’s attempts to seize Ukrainian land will not be acknowledged and said harsher sanctions need to be enforced.