Ukrainian forces have pushed into Russian-occupied areas in northern Donetsk in a move the U.K. defense ministry on Friday said is "putting pressure on territory Russia considers essential to its war aims."

Fighting in northern Donestk has been described as "ongoing," as Ukrainian forces launch a counteroffensive on the town of Lyman, which Russia has occupied since May.

Lyman is roughly 30 miles east of Izyum in the northeastern region of Kharkiv, where Ukrainian troops saw major gains this month by retaking the majority of the occupied territory and forcing Russian soldiers to retreat.

Ukraine announced control over the entire region west of the Oskil River, where territory remains contested from eastern Kharkiv through the Luhansk regions.

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Kharkiv soldiers

Armed national guard servicemen walk along a trench at one of the sections of a defense line outside Kharkiv, Kharkiv Region, northeastern Ukraine, in August. (Vyacheslav Madiyevskyy/ Ukrinform/Future Publishing via Getty Images)

"Russia attempted to "integrate" the Oskil into a consolidated defensive line following its forces’ withdrawals earlier in the month," the U.K. defense ministry said Friday.

However, over the last three days, Ukrainian forces have "secured bridgeheads on the east bank" of the dividing river, suggesting they could be in a better position to retake the rest of Kharkiv before advancing into Luhansk.

The ministry’s announcement comes as Russia launches referendums in Donetsk, Luhansk, Zaporizhzhia and Kherson, despite intense fighting in all four regions. 

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Kharkiv was previously listed as one of the regions Russia intended to annex.

Western officials have condemned Moscow’s push to illegally seize Ukrainian territory by holding what they have called "sham" elections in eastern and southern Ukraine. 

"Voting" will begin Friday and polling stations will be opened Tuesday. 

According to Russia-state owned media outlet, RIA, the question on the ballot will allegedly read, "Do you support secession from Ukraine, formation of the region as an independent state and joining Russia?"

Ukrainian soldiers

Ukrainian soldiers are seen riding on an armored personnel carrier during an exercise not far from Kharkiv on April 30. (SERGEY BOBOK/AFP via Getty Images)

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Preliminary results will reportedly be released on Tuesday and Wednesday.

Ukrainian President Volodymyr Zelenskyy condemned the election as a "farse" and Western officials have repeatedly pointed to similar step Russia took during its 2014 invasion of Crimea.