Ukraine announced that its forces have retaken three villages in the eastern region of Donetsk, the first reported gains of their new offensive.
But three people were killed and at least another 23 wounded as Russia shelled a rescue boat evacuating civilians from Russian-controlled territory, the Kherson region prosecutors' office said on Sunday.
"On the morning of June 4, the enemy launched a full-scale offensive on five sectors of the front in the direction of the southern Donetsk region," the ministry said in a statement, adding that "the enemy did not achieve its goal and did not succeed."
The ministry said that the Ukrainian army led the offensive with six mechanized battalions and two tank battalions.
Russia said Monday it had repelled "a large-scale offensive" by Ukrainian forces in Moscow-annexed Donetsk, as fighting intensified along their border.
Kiev has for months said it is preparing a major counteroffensive, hoping to reclaim territory lost since Russia launched its military operation in February 2022.