KYIV (Reuters) -Ukraine’s top commander warned on Friday of “heavy battles” looming on the war’s new front in the northeastern Kharkiv region as Russian President Vladimir Putin said Moscow was carving out a “buffer zone” in the area.

Russian forces attacked the Kharkiv region’s north last Friday, making inroads of up to 10 kilometres (6 miles) and unbalancing Kyiv’s outnumbered troops who are trying to hold the line over a sprawling front nearly 27 months since the invasion.

Colonel-General Oleksandr Syrskyi said the attack had expanded the combat zone by around 70km and that Russia had launched its incursion ahead of schedule after “it noticed the deployment of our forces”.

“We understand there will be heavy battles and that the enemy is…