Ukrainian forces hung on to positions in the ruined eastern city of Bakhmut on Thursday, while Moscow said its security forces were battling Ukrainian saboteurs who had taken hostages in a cross-border raid.

Moscow said a group of armed Ukrainians had crossed into Russia’s Bryansk province and fired on a car, killing one and wounding a child. They were holding hostages in a shop near the border.

In a brief TV address, President Vladimir Putin said the attackers had deliberately fired on the car knowing it held civilians.

“They won’t achieve anything. We will crush them,” he said, saying Russia was fighting “terrorists and neo-Nazis”.

An aide to Ukrainian President Volodymyr Zelensky called the reports a false provocation by Moscow, but also appeared to imply some form of incident had been carried out by partisans.

Near the front lines west of Bakhmut, in the Ukrainian-held town of Chasiv Yar, the thump of outgoing artillery fire could be heard.

In nearby towns and villages, new trenches had been dug on the roadside 20-40 metres apart, an apparent sign that Ukrainian forces were strengthening defensive positions west of the city.

The boss of Russia’s Wagner private army, Yevgeny Prigozhin, released a video of his men waving a Wagner banner and musical instruments atop a ruined multi-storey building, which he said had been filmed near the centre of Bakhmut.

Bakhmut has been reduced to a blasted wasteland, with a few thousand of its 70,000 prewar civilian population still living inside as armies battle street-by-street.

Russian troops, bolstered by hundreds of thousands of reservists called up last year and tens of thousands of convicts recruited by Wagner from prison, have been advancing north and south of the city, to cut off the remaining routes in.

Moscow, which lost captured territory throughout the second half of 2022, says taking Bakhmut would be a step towards seizing the rest of the surrounding Donbas region, a major aim.