Ukrainian troops are preparing to enter the southern city of Kherson after Russian forces retreated across the Dnieper River, a spokesperson for Ukraine's military intelligence agency said.

Andriy Yusov told The Associated Press that an operation to liberate Kherson" and the surrounding region of the same name was underway Friday.

But it will be possible to talk about establishing Ukrainian control over the city only after an official report by the General Staff of the Ukrainian army, Yusov said.

Videos posted on social media showed a Ukrainian flag flying in a central square for the first time since early March, when the city was seized by the Russians. Kherson was the only regional capital captured by Russian forces after they invaded Ukraine in late February.

Their withdrawal marks a major victory for Ukraine, although Russia maintains control of about 70% of the Kherson region.

Kremlin spokesman Dmitry Peskov on Friday said Moscow continues to consider Kherson as part of Russia despite the troop withdrawal, and rejected the notion that the retreat is humiliating for President Vladimir Putin.