KIEV (Xinhua) -- Adviser to Ukrainian President Oleksiy Aristovich on Monday described the Ukrainian military operation in the main cities of the eastern Luhansk region as "successful."

"The defense of Lysichansk-Severodonetsk is a successful military operation," Aristovich wrote on Facebook.

He added that Ukraine carried out all four main tasks of the defensive operation, including intercepting the main enemy forces, inflicting losses on enemy forces, buying time to receive weapons, and creating conditions for offensive operations in other sectors of the front line.

Aristovich said that Ukraine is currently conducting counter-offensive operations in the eastern Donetsk region and in the southern regions of Kherson and Zaporizhia.

On Sunday, Russian Defense Minister Sergei Shoigu informed President Vladimir Putin of taking control of the Lugansk region, according to the Russian Defense Ministry.

Ukrainian President Volodymyr Zelensky late Sunday confirmed the withdrawal of Ukrainian forces from Lysychansk, a major city in Luhansk, but vowed that Ukrainian forces would "come back".