Ukraine’s armed forces on Saturday said they had "liberated" five settlements in the Donetsk region and encircled thousands of Russian soldiers near the eastern town of Lyman.

"The Russian troops in the area of Lyman are encircled. Yampil, Novoselivka, Shandryholove, Drobysheve, and Stavky settlements are liberated. Stabilization measures are being conducted there," Serhii Cherevatyi, Speaker of the Eastern group of troops, told a Ukrainian news outlet reported Pravda.

The advancement comes one day after Russian President Vladimir Putin declared a land grab for not only Donetsk but the Luhansk, Zaporizhzhia and Kherson regions as well. 

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Putin warned that Russia will now treat any attack on the four regions as an attack on mainland Russia, calling the Ukrainians still residing in the war-torn regions "forever" Russians.

But Ukrainian forces have been making advances in western Luhansk and northern Donetsk as they inch towards the strategically important city of Sievierodonetsk, which Russia has occupied since June.

Cherevatyi said that some 5,000 to 5,500 occupiers were in Lyman, but noted it was difficult to estimate the number of troops in the areas surrounding the town due to the fluid movement of troops in combat zones. 

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The spokesman said that some Russian troops have tried to unsuccessfully break through Ukraine’s barricade near the city while others had begun to surrender. 

Taking Lyman would be a significant strategic win for Ukraine but Cherevatyi said the fight to fully liberate the city was not over. 

Lyman has served as a major logistics and transport hub for Russian forces and its operations in northern Donetsk, reported Reuters.

Securing the city would be the biggest battlefield win for Ukraine since it forced Russian troops to withdraw from roughly the entire Kharkiv region in a major counter-offensive last month.