Both sides have been pouring forces into the region which threatens Kharkiv, Ukraine’s second city with a population of 1.3 million, for the first time since 2022.

Ukrainian officials confirmed heavy fighting but denied that Russian forces had captured Vovchansk.

“There are active shooting battles on the northern outskirts of the city,” said Oleh Syniehubov, head of the Kharkiv Regional Administration.

Kharkiv will come into range of Russia’s artillery if its forces can push a few miles further south, but the British Ministry of Defence said that the assault was probably planned as a diversion to pull Ukrainian forces away from battlefields in Donbas, the focus of further potential Russian attacks.

“It is unlikely that Russia has built up sufficient combat power to the city without diverting additional forces into the area,” it said.

Thousands of people have evacuated from villages near the Ukraine-Russia border since Friday and reports also now state that women and children were fleeing Kharkiv.