Ukraine said Thursday thatin 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 Feb. 24, United Nations Secretary-General António Guterres visited towns outside the capital of Kyiv, including Bucha, where evidence of mass killings of civilians was found after Russia's retreat from the area.
"Ukraine is an epicenter of unbearable heartache and pain," Guterres told reporters in Kyiv, alongside Ukraine's President Volodymyr Zelenskyy. Guterres' visit came two days after hewith Russia's President Vladimir Putin in Moscow.
, Poland and Bulgaria, 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. The most intense 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.
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.
Ukrainian Special Forces Battalion Commander Ihor Lapin told CBS News correspondent Charlie D'Agata, who's, his troops simply don't have the firepower to match Russia. The need for more high-caliber ammunition is urgent, he said, adding that the fighting's been so intense, the Russians launched 1500 mortars on a single position in a single day.
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 analyzed by The Associated Press also showed evidence of intense Russian fire on Mariupol in recent days. The images show how concentrated attacks have greatly damaged a central facility at the Azovstal steelworks, the last holdout of Ukrainian fighters in the key battleground port city.
An estimated 1,000 civilians are sheltering along with about 2,000 Ukrainian fighters in the steelworks, a massive Soviet-era complex with complex 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, Guterres on Thursday toured towns outside Kyiv 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."
After visiting the town of Borodianka, he told local press, "The war is an absurdity in the 21st century. The war is evil. And when one sees these situations our heart, of course, stays with the victims."
Evidence of atrocities was discovered in the towns after the Russians retreated from the area in the face a fiercer than expected Ukrainian resistance, bolstered by Western arms.
Guterres spoke of "the senseless loss of life, the massive destruction, the unacceptable violations of human rights and the laws of war."
"I am here to focus on ways on how the U.N. can expand support for the people of Ukraine, saving lives, reduce suffering and help find the path of peace," he said. "I want the Ukrainian people to know that the world sees you, hears you, and is in awe of your resilience and resolve."
He pledged to increase U.N. efforts to provide "life-saving humanitarian aid" to millions of civilians inside Ukraine. "This war must end, and peace must established in line the charter of the United Nations and international law. Many leaders have made many good efforts to stop the fighting, though these efforts, so far, have not succeeded."
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 organizations reported.
Ukraine has urged its allies to send even more military equipment so it can continue its fight.
NATO chief Jens Stoltenberg said Thursday that "to date, NATO allies have pledged and provided at least 8 billion U.S. dollars in military support to Ukraine. And we see the importance of further stepping up our support to Ukraine."
He also said Finland and Sweden would be embraced with open arms should they decide to join the 30-nation military organization and could become members quite quickly.
While Russia's initial blitz was stunted — and it suffered the humiliating— Britain's Defense Ministry said the Russian navy still has the ability to strike coastal targets in Ukraine.
In an intelligence briefing posted Thursday morning, the ministry says that about 20 Russia naval vessels, including submarines, are currently operating the Black Sea zone.
But the ministry says Russia isn't 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.
While it presses its campaign in the east, Moscow has also piled on the pressure by leveraging its biggest export product, energy, cutting off NATO members Poland and Bulgaria from its natural gas on Wednesday.
European leaders blasted that decision as "blackmail," saying the move and the Kremlin's warning that it might cease shipments to other countries is a failed attempt to divide the West over its support for Ukraine.
The tactic against the two EU countries could eventually force targeted nations to ration gas and deal another blow to economies suffering from rising prices. At the same time, it could deprive Russia of badly needed income to fund its war effort.
The gas cuts do not immediately put the two countries in any dire trouble. Poland, especially, has been working for many years to line up other suppliers, and the continent is heading into summer, making gas less essential for households.
Still, the cutoff and the Kremlin warning that other countries could be next sent shivers of worry through the 27-nation European Union. Germany is the world's biggest buyer of Russian energy, and Italy is also a significant consumer, though they, too, have been taking steps to reduce their dependence on Moscow.
An independent research group said Thursday that Germany was the biggest buyer of Russian energy during the first two months of the war in Ukraine. The study published by the Centre for Research on Energy and Clean Air calculates that Moscow Russia has earned 63 billion euros ($66.5 billion) from fossil fuel exports since Feb. 24, the date Russian troops attacked Ukraine.
CBS News correspondent Pamela Falk contributed reporting from the United Nations.
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