Ukraine's military says Russian troops have crossed the border into the eastern region of Kharkiv, most likely to establish a buffer zone between the two countries.

The regional governor said on social media on Friday that the Russians have started a new stage of their offensive in northern Kharkiv.

The governor said an area near the border with Russia came under heavy shelling, killing two civilians.

An official of the Ukrainian military's General Staff told NHK that Russian troops have entered from the north, and pushed one kilometer into the region.

The official said the scale of the incursion suggests that the objective is not to seize the city of Kharkiv, but to create a 10-kilometer wide buffer zone along the border to prevent Ukrainian shelling into Russian territory.

Ukrainian President Volodymyr Zelenskyy told reporters that "Russia has begun a new wave of counteroffensive actions in this direction."

He stressed that Ukraine was prepared for the attack and fought back with brigades and artillery.

Diplomatic sources in Kyiv say this is believed to be the first Russian incursion into the Kharkiv region since Ukrainian forces recaptured most of the territory in September 2022.