Russian tanks and troops have begun advancing into Sievierodonetsk, the largest city in Donbas still held by Ukraine, witnesses and officials have said.

“Unfortunately we have disappointing news: the enemy is moving into the city,” the Luhansk regional governor, Serhiy Gaidai, told Ukrainian national television on Monday.

Witnesses said Russian tanks were advancing towards the centre of the city one blast at a time, razing everything in their path that remains following intense shelling that Ukrainian authorities have said has led to conditions on the ground reminiscent of Mariupol.

“They [the Russian army] use the same tactics over and over again,” Gaidai said. “They shell for several hours – for three, four, five hours – in a row and then attack. Those who attack die. Then the shelling and attack follow again, and so until they break through somewhere.”