The UN Human Rights Council announced it will convene a special session to address alleged Russian human rights violations during its war in Ukraine.
More than 50 countries backed a request from Kyiv and demanded an extraordinary meeting of the UN's top rights body to examine "the deteriorating human rights situation in Ukraine stemming from the Russian aggression".
Yevheniia Filipenko, Ukraine's ambassador to the UN in Geneva, said it would send a strong signal to Russian President Vladimir Putin about Moscow's international isolation.
"Together, we are sending another strong message to Putin and his clique of war criminals: you are isolated as never before," she said in a video message on Twitter.
The meeting will convene at 9am on Thursday and be webcast live in the six official UN languages.
The support of 16 members of the council - a third of the membership - is required to convene a special session.
Russia was a member of the Human Rights Council until the UN General Assembly in New York voted on 7 April to suspend them from the body and from sitting in judgement of other nations' human rights records.
Russia then immediately withdrew from the council.
The announcement comes after Ukrainian officials said that Russian forces have stormed the Azovstal steel plant in Ukraine's strategic port of Mariupol and stepped up missile strikes elsewhere.
Meanwhile, Russian President Vladimir Putin oversaw a parade of military firepower in Moscow, marking the anniversary of the Soviet Union's victory over Nazi Germany in World War Two.
Mr Putin told his armed forces they were fighting for their country but he did not say how much longer their assault on Ukraine, now in its 11th week, would last or how it would end.
Ukraine's President Volodymyr Zelensky, in his own Victory Day address, said his country would triumph over Russian forces.
"On the Day of Victory over Nazism, we are fighting for a new victory. The road to it is difficult, but we have no doubt that we will win," he said in a video address to mark the deaths of more than eight million Ukrainians in World War II.
Ukrainian officials said heavy fighting was underway in the country's east, while four high-precision Onyx missiles fired from the Russian-controlled Crimea peninsula had struck the Odessa area in southwestern Ukraine.
The governor of Mykolaiv, also in the southwest, said overnight strikes were very heavy.
Azovstal, a vast complex of buildings and underground tunnels, is the last holdout for Ukrainian troops in Mariupol, whose capture would help link Russian-seized areas in southern and eastern Ukraine and cut Ukraine off from the Azov Sea.
Mr Putin has already declared victory in Mariupol but control of the steel plant would be a symbolic achievement on the 75th day of a war that has cost many Russian lives and isolated its economy, but failed to capture any major city.
The Russian president had told his defence minister not to storm Azovstal to avoid loss of Russian lives but Ukraine's defence ministry said Russian forces backed by tanks and artillery were conducting "storming operations".
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Moscow has denied previous Ukrainian allegations of storming the complex, where civilians have also been sheltering.
On Saturday Kyiv and Moscow said all the civilians had now been evacuated from the facility, but there are still people hoping to flee the wider city of Mariupol.
"There's lots of people still in Mariupol who want to leave but can't," evacuee Viktoria Andreyeva, a 46-year-old history teacher, said in the Ukrainian-controlled city of Zaporizhzhia, about 230km northwest of Mariupol.
Russian TV schedules hijacked
Just before the troops and tanks paraded in Moscow's Red Square, Russian satellite television schedules were altered to show viewers in the Russian capital messages condemning the war in Ukraine.
"The TV and the authorities are lying. No to war," screenshots obtained by Reuters showed before they disappeared.
Russian forces have devastated villages, towns and cities and driven nearly six million Ukrainians to flee since they invaded Ukraine on 24 February.
Ukraine's Deputy Defence Minister Hanna Malyar said Russian forces were now trying to advance in eastern Ukraine, where the situation was "difficult", but had moved back from the city of Kharkiv, where a local official reported heavy Russian shelling.
Three more civilians were killed in Kharkiv and three in the Luhansk region, its governor Serhiy Gaidai said. It was not immediately possible to verify the reports.
"Today we do not know what to expect from the enemy, what terrible thing they might do, so please go out onto the street as little as possible, stay in the shelters," he said.
Mr Putin said Russia's "special military operation" in Ukraine was a purely defensive and unavoidable measure against plans for a NATO-backed invasion of lands he said were historically Russia's, including Crimea.
"Russia preventively rebuffed the aggressor," he said, offering no evidence for what he called open preparations to attack Crimea and Ukraine's Donbas region.
In 2014, Russian-backed separatists seized parts of Donbas in eastern Ukraine and Russia annexed Crimea from Ukraine the same year.
Moscow then massed troops around Ukraine last year ahead of an all-out invasion that Kyiv and its Western allies say was entirely unprovoked.
"NATO countries were not going to attack Russia. Ukraine did not plan to attack Crimea," Ukrainian senior presidential adviser Mykhailo Podolyak said after Putin's comments.
Ukrainians being taken against their will into Russia
The Pentagon said on Monday that it has seen indications that Ukrainians caught up in Russia's invasion are being forcibly removed from their homeland and sent to Russia.
"I can't speak to how many camps or what they look like," Pentagon spokesman John Kirby told reporters when asked about statements from Kyiv that some 1.2 million Ukrainians were being sent to Russia and placed in camps.
"But we do have indications that Ukrainians are being taken against their will into Russia," Kirby said. He called these actions "unconscionable" and "not the behavior of a responsible power".
The deportation of Ukrainians from their own nation - often to isolated or economically depressed regions of Russia, according to Kyiv - is another indication that Russia's President Vladimir Putin "simply won't accept and respect Ukrainian sovereignty".
Ukraine's President Volodymyr Zelensky said back in early April, six weeks after Russia launched its deadly invasion, that thousands of Ukrainians had been sent to Russian territory.
But that figure has since ballooned to more than 1.19 million, including at least 200,000 children, Ukraine's ombudswoman Lyudmyla Denisova said.
Kirby stopped short of describing the deportations as ethnic cleansing, stressing it was not the Pentagon's place to make such determinations. But he said there was abundant evidence of "Russian brutality" during the war.
Moscow has had "75 days of brutalising the nation of Ukraine and the Ukrainian people," he said. "And every time you think they just can't fall to a new low, they prove you wrong."
EU close to embargo on oil
Moscow has come under increasingly punishing sanctions since its invasion, with trade heavily impacted and assets seized.
A German official said agreement by European Union member states on new measures - expected to include an embargo on Russian oil - was close.
The EU's foreign policy chief told the Financial Times the bloc should also consider using frozen Russian foreign exchange reserves to help pay for the cost of rebuilding Ukraine after the war.
Charles Michel, president of the European Council visited Odessa in the latest show of Western support, while Council of Europe Secretary General Marija Pejcinovic was in Kyiv to discuss what Ukraine said was how to hold Russia accountable for its crimes.