RUSSIA’S fresh offensive in eastern Ukraine gathered momentum today as United Nations secretary-general Antonio Guterres visited towns outside Kiev badly affected  by the war’s first phase.

Mr Guterres condemned alleged atrocities in towns such as Bucha, where evidence of mass killings of civilians was found after Russian troops retreated.

“Wherever there is a war, the highest price is paid by civilians,” he said as he visited the bombed-out Kiev suburb of Irpin.

“But when we talk about war crimes, we cannot forget that the worst of crimes is war itself,” he added while visiting Bucha.

Touring Borodyanka, another scene of alleged atrocities outside Kiev, Bulgarian Prime Minister Kiril Petkov vowed that his country would join others in providing military assistance to the Ukrainian government.

“This is not just the battle for Ukraine, but it is a matter for civilisation to choose which side to take,” he claimed, the day after Russia suddenly cut off natural gas to Bulgaria and fellow Nato member Poland.

Forced to regroup after failing to take the capital, Russia has switched its focus to the vital eastern industrial heartland, where fighting is now intensifying.

The General Staff of Ukraine’s military said today that Russian forces were “exerting intense fire” in several places in the Donbass, claiming that Kiev’s forces have repelled six attacks in the region over the past 24 hours.

The most intensive action was around Donetsk and close to Kharkiv, which lies outside the Donbass but is seen as key to Russia’s apparent bid to encircle Ukrainian troops there.

Lugansk Governor Serhiy Haidai said that, in addition, the Russian army had heavily shelled residential areas in his region, also in the Donbass, adding that four civilians had died in the past day and four more had been wounded.

Satellite images showed evidence of intense Russian fire on Mariupol in recent days, including heavy damage to a central facility at the Azovstal steelworks, the last redoubt of far-right Ukrainian fighters in the south-eastern port city.

Ukrainian authorities warned that civilians remaining trapped there face dangerously unsanitary conditions, with a risk of diseases like cholera and dysentery, while many of the dead from a two-month siege remain unburied.

Russia, meanwhile, said that the southern city of Kherson, which its forces control, had come under fire that hit a television tower on Wednesday night, knocking Russian channels off the air.

Nato secretary-general Jens Stoltenberg said today that “to date, Nato allies have pledged and provided at least $8 billion [£6.4bn] in military support to Ukraine.”