Ukrainian troops advance, forcing Russian withdrawal from key areas

Sept. 10 (UPI) -- Ukrainian forces made major gains in the eastern part of the country Saturday, with Russian soldiers withdrawing from strategic towns, retreating from a rapid counterattack.

Ukrainian troops entered the city of Kupiansk on Saturday, a strategic supply hub for Russian forces in of eastern Ukraine, Russia's defense ministry confirmed Saturday.

Kupiansk is a town of about 27,000 people in eastern Ukraine.

Russia also confirmed its troops have retreated from the nearby town of Izyum.

Izyum sits near the border between the Kharkiv and Donetsk regions and had a pre-war population of about 45,000 and served as a staging ground for Russian military operations.

"Russian forces were likely taken by surprise. The sector was only lightly held and Ukrainian units have captured or surrounded several towns," the U.K. Ministry of Defense said on Twitter.

"With Ukrainian operations also continuing in Kherson, the Russian defensive front is under pressure on both its northern and southern flanks."

Soldiers posted video on social media of troops entering the city victoriously.

"The town of Balakliya, Kharkiv region, is liberated by Ukrainian troops!," the Ministry of Defense of Ukraine said in a statement on Saturday.

"The Commander of Ukrainian Land Forces, Hero of Ukraine, Colonel General Oleksandr Syrskyi is leading the Ukrainian offensive in this sector. The Ukrainian flag has been raised in the town center."

Moscow is reportedly sending reinforcements in the wake of the Ukrainian military advances.

Moscow is moving troops and equipment to the region, CNN reported Saturday.

The outlet quoted a Russian photographer as saying Russian helicopters were unloading an armored vehicle in Kharkiv and redeploying reserve troops.

"The helicopters are dropping in at landing points all along the line of contact. ... The reinforcements will help to stop any further advance of the Kyiv regime," Yevgeniy Poddubny told CNN.

The news comes a day after Ukrainian President Volodymyr Zelensky said that his forces have reclaimed almost 400 square miles of territory from Russia over the past week, including a counteroffensive that won back a settlement in Kharkiv.

Ukrainian forces took back control of the settlement, Shevchenkove, and put them in a position to go after the Russian stronghold of Kupyansk in the northeast, officials said on Friday.