"Ukrainian forces are "shifting to offensive actions" in some areas," Deputy Defence Minister of Ukraine Hanna Malyar said, APA reports citing BBC.
Ukrainian military sources told the BBC that a series of small scale armoured offensive operations are under way.
They did not say whether this was the start of Ukraine's long awaited full scale counter-offensive.
Earlier, Russia's defence ministry said it thwarted a major Ukrainian attack in Donetsk.
Malyar described the eastern city of Bakhmut as the "epicentre of hostilities", and claimed Russian forces were on the defence there as well as in the south.
The commander of Ukraine's ground forces, Gen Oleksandr Syrskyi, said troops were "moving forward" towards Bakhmut and had destroyed a Russian position near the city.