Senior Ukrainian presidential adviser Oleksiy Arestovych has claimed that Ukrainian forces have broken through Russian lines in several places near the southern city of Kherson, as they press a new campaign to retake territory.

"I should note today the (Russian) defenses were broken through in a few hours," Arestovych was quoted by Reuters as saying.

Earlier on Monday, Russia's defense ministry said that Ukrainian troops had attempted an offensive in the Mykolaiv and Kherson regions, but sustained significant casualties, according to RIA news agency.

(With input from Reuters)