Ukrainian President Volodymyr Zelenskyy has visited the city of Kherson, which Ukrainian forces have taken back from Russia.

Zelenskyy posted a photo of himself cheering Ukrainian troops. Local media have reported that Zelenskyy told them, "We are moving forward."

The Russian military claimed to have taken full control of the Kherson region in March. The Kremlin then unilaterally annexed Kherson and three other regions in September.

The Russian military has withdrawn from the city and other parts of the region after an intense counteroffensive by Ukrainian forces.

Ukrainian troops and administrative officials have returned to the city to stabilize the situation there.

Zelenskyy said on Sunday that the fighting in the Donetsk region remains as intense as it has been in previous days. He said the level of Russian attacks is not decreasing. But he said the level of resilience and bravery of Ukrainian fighters is the highest.

The Institute for the Study of War, a US think tank, says Ukraine has won an important victory in the campaign that liberated the western Kherson region.

It says Ukraine's success resulted in large part from the Ukrainian Armed Forces' innovative use of the US-provided HIMARS precision rocket system to disrupt Russian supply lines.

The think tank is of the opinion that Putin likely let the Russian commander withdraw from western Kherson "on condition that he takes the rest of the Donetsk region using Russian forces recouped from western Kherson."

It adds "Russian offensive operations in the Donetsk region will intensify in the coming weeks as additional mobilized servicemen arrive along with forces withdrawn from western Kherson."