Ukrainian forces say they have regained control of the east bank of the River Oskil, seen as the front line with Russian troops in north-east Ukraine.
Russia’s army has been almost completely pushed out of the Kharkiv region and a regional leader said the next target would be neighbouring Luhansk.
President Volodymyr Zelensky said the next offensive was being prepared.
Meanwhile, Russia was accused of targeting a nuclear plant in the south.
Ukrainian nuclear operator Enerhoatom said a rocket landed 300m (1,000ft) from nuclear reactors at the the country’s second largest plant in Mykolayiv region, damaging buildings and shutting down part of a hydro-electric power station at the complex.
The attack has not been independently confirmed, although footage was posted online by the Ukrainian military.
