Kyiv said on Monday it was conducting "offensive actions" on the front line and noted some progress in the eastern Ukrainian city of Bakhmut.
The announcement from the defence ministry came after Russia said it had repelled "a large-scale offensive" by Ukrainian forces in the Moscow-occupied Donetsk region.
"The defensive operation includes counteroffensive actions. Therefore, in some sectors, we are conducting offensive actions," Deputy Defence Minister Ganna Malyar said.
"The Bakhmut sector remains the epicentre of the hostilities," she said, adding Kyiv's troops were occupying the "dominant heights" and reported some "success".
"In the south the enemy is on the defensive," she added.
The Russian mercenary group Wagner, who has led the assault for Bakmut, said in May it seized the now ravaged city after the longest and bloodiest fight of the offensive.
Wagner boss Yevgeny Prigozhin said on Monday that Ukraine's troops had made gains near Bakhmut.
Russian troops, he said, were "slowly" leaving parts of the village of Berkhivka near Bakhmut.
Malyar also said Russia was "actively spreading information about a counteroffensive" to "divert attention from defeats in the Bakhmut sector."