A senior US government official says Russian forces may step up their offensive in the eastern Ukrainian region of Kharkiv with the goal of establishing a buffer zone.

The regional governor said on social media on Friday that an area near the border with Russia came under heavy shelling and that the Russians have started a new stage of their offensive in northern Kharkiv.

An official of the Ukrainian military's General Staff told NHK that Russian ground troops have crossed the border from the north and entered Kharkiv.

The official said the move suggests the objective is to create a buffer zone along the border to prevent Ukrainian shelling into Russian territory.

Meanwhile, White House national security spokesperson John Kirby told reporters on Friday that Russia will likely increase the intensity of its offensive in the coming weeks, committing additional troops in an attempt to establish a buffer zone along the Ukrainian border.

He said President Joe Biden signed another 400-million-dollar drawdown package for Ukraine, which he says includes additional munitions for Patriot air defense systems.

Kirby added, "We do not anticipate any major breakthroughs and over time, the influx of US assistance will enable Ukraine to withstand these attacks over the course of 2024."