Ukraine said that Russia’s offensive in the east picked up momentum, with several towns coming under intense attack as Moscow’s forces attempt to surround Ukrainian troops.

In a reminder of the horrific toll the war has taken since it began February 24, United Nations secretary-general Antonio Guterres visited towns outside the capital of Kyiv where evidence of mass killings of civilians was found after Russia’s retreat from the area.

The fighting gathered pace after Russia suddenly cut off natural gas to two Nato nations on Wednesday, in what was seen as a bid to punish and divide the West over its support for Ukraine ahead of the potentially pivotal battle in the eastern industrial region of the Donbas.

The general staff of Ukraine’s military said Russian forces were “exerting intense fire” in several places as they pushed on with the second phase of their invasion.

(PA Graphics)

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

Tatiana Pirogova spoke of the intense fear of living under constant bombardment.

“It’s not just scary. It’s when your stomach contracts from pain,” the Kharkiv resident said.

“When they shoot during the day, it’s still OK, but when the evening comes, I can’t describe how scary it is.”

The general staff said that over the past 24 hours, the Ukrainian forces have repelled six attacks in the Donbas, control of which is now Moscow’s primary focus ever since its initial offensive faltered and failed to take the Ukrainian capital.

Luhansk governor Serhiy Haidai said the Russian army shelled the residential area in his region “29 times by aircrafts, multiple rocket launches, tube artillery and mortars”.

Satellite photos also showed evidence of intense Russian fire on Mariupol in recent days.

Russia Ukraine
Damage at the Azovstal steelworks in Mariupol (Planet Labs PBC/AP)

The images show how concentrated attacks have greatly damaged a central facility at the Azovstal steelworks, the last redoubt of Ukrainian fighters in the key battleground city.

An estimated 1,000 civilians are sheltering along with about 2,000 Ukrainian fighters in the steelworks, a massive Soviet-era complex with a warren of underground facilities built to withstand airstrikes.

Russia, meanwhile, said a city under its control in the south also came under fire.

With the war now in its third month, Mr Guterres toured towns outside Kyiv, including Bucha, that have seen some of the most horrific attacks of the war.

“Civilians always pay the highest price,” he said as he visited the bombed out suburb of Irpin.

“And this is something everyone should remember, everywhere in the world.

“Wherever there is a war the highest price is paid by civilians.”

UN secretary-general Antonio Guterres, centre, stands on the side of a mass grave in Bucha, on the outskirts of Kyiv, Ukraine (Efrem Lukatsky/AP)
UN secretary-general Antonio Guterres, centre, stands on the side of a mass grave in Bucha, on the outskirts of Kyiv, Ukraine (Efrem Lukatsky/AP)

Evidence of atrocities was discovered in the towns Mr Guterres visited on Thursday after the Russians retreated from the area in the face a fiercer than expected Ukrainian resistance, bolstered by Western arms.

In what could be a further Ukrainian counterattack, a series of explosions boomed near the television tower late Wednesday in southern Ukraine’s Kherson, which has been occupied by Russian forces since early in the war.

The blasts at least temporarily knocked Russian channels off the air, Ukrainian and Russian news organisations reported.

Ukraine has urged its allies to send even more military equipment so it can continue its fight.

Nato chief Jens Stoltenberg said that “up to date, Nato allies have pledged and provided at least eight billion US dollars in military support to Ukraine.

“And we see the importance of further stepping up our support to Ukraine.”

While Russia’s initial blitz was stunted, and it suffered the humiliating loss of a massive warship, Britain’s Ministry of Defence said the Russian navy still has the ability to strike coastal targets in Ukraine.

In an intelligence briefing, the ministry says that about 20 Russia naval vessels, including submarines, are currently operating the Black Sea zone.

But the ministry says Russia is not able to replace the guided-missile cruiser Moskva, which sank earlier this month in the Black Sea, because the Bosporus Strait remains closed to all non-Turkish warships.

Russia also lost the landing ship Saratov, which was destroyed by explosions and fire on March 24.