The head of the United Nations has visited Ukrainian towns where evidence of mass killings of civilians was uncovered after Russian forces retreated.
UN Secretary-General Antonio Guterres toured towns outside the capital Kyiv, including Bucha, which have witnessed some of the most horrific violence during the war.
"Civilians always pay the highest price," he said, as he visited the heavily-bombed 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."
He made the remarks two days after meeting with Russian President Vladimir Putin in Moscow, during which the UN said they had agreed on arranging evacuations from a besieged steel plant in the city of Mariupol.
Earlier in the day he met with Russian Foreign Minister Sergei Lavrov, who claimed Moscow was effectively at war with NATO and said the threat of a nuclear conflict "should not be underestimated".
Meanwhile, Ukraine said Russia's offensive in the east had picked up momentum, with several towns coming under intense attack.
Moscow's forces were attempting to surround Ukrainian troops after Russia suddenly cut off natural gas to Poland and Bulgaria, two Nato nations, on Wednesday, in what is considered a bid to punish and divide the west over its support for Ukraine.
Russia pushes second phase of invasion
The general staff of Ukraine's military said Russian forces were "exerting intense fire" as they pushed on with the second phase of their invasion.
The most intense fighting was seen around Donetsk and close to Kharkiv, which lies outside the Donbas region but is seen as key to Russia's apparent attempt to encircle Ukrainian troops there.
The general staff said Ukrainian forces have repelled six attacks in the Donbas in the past 24 hours.
The governor of Luhansk, Serhiy Haidai, said Russian forces had shelled the residential area in his region "29 times by aircraft, multiple rocket launches, tube artillery and mortars".
Fighting at the Azovstal steelworks
Satellite photos show extensive damage to a central facility at the Azovstal steelworks, where Ukrainian fighters are holding out in the key battleground city of Mariupol.
Around 1,000 civilians are estimated to be sheltering with about 2,000 Ukrainian fighters in the large Soviet-era complex.
The Donetsk region's governor, Pavlo Kyrylenko, said Russia was not allowing wounded Ukrainian fighters to be evacuated from the steelworks. He also accused Moscow of not allowing humanitarian corridors to be established to evacuate civilians from the region.
Russia's fleet still a threat
It comes as the UK Ministry of Defence (MoD) said Russia's Black Sea fleet retains the ability to strike coastal targets despite the losses of its landing ship Saratov and cruiser Moskva.
The MoD said around 20 Russian Navy vessels, including submarines, are in the Black Sea operational zone.
"The Bosphorus Strait remains closed to all non-Turkish warships, rendering Russia unable to replace its lost cruiser Moskva in the Black Sea," it added.