"We are restoring full control over the region. We have three settlements left on the Kinburn Split to officially no longer be a region at war," said Mykolaiv regional governor Vitaly Kim on social media.
His announcement comes after a defense ministry spokeswoman confirmed this week that Ukrainian forces were carrying out "a military operation" on the Kinburn Split.
The southern split jutting into the Black Sea is divided in two: in the west, as part of the Mykolaiv region and to the east as part of the Kherson region.
It is cut off from territory controlled by Ukraine's forces by the Dnipro river, which flows through the Kherson region.
Kherson's capital, recently recaptured by Ukraine, lies on the west bank while the Russian forces are entrenched in the eastern side.
Kherson fell quickly and early to Russian forces after they invaded in February but the invading forces were stopped in Mykolaiv as they pushed further west.
But Kyiv's troops have been pushing out Russian forces from the southern Mykolaiv and Kherson regions and recently recaptured Kherson city, which was the only regional capital Moscow's forces had taken since February.
"As soon as there is a result, we will report on it," said southern army command spokeswoman Natalia Gumeniuk.