The United States raised the alarm Wednesday over the "staggering" human cost of Moscow's invasion of Ukraine, as the apparent deployment of cluster bombs and other treaty-violating weapons raised fears of a brutal escalation in the week-old conflict.
The American warnings came as Russia revealed 498 of its troops had been killed in the assault on ex-Soviet Ukraine -- the first official death toll it has given and one Kyiv says is by far an undercount.
And they came on the eve of the resumption of ceasefire talks after a first round Monday failed to produce a breakthrough.
On the ground in Ukraine, Russia appeared despite determined resistance to be intensifying the offensive ordered seven days earlier by President Vladimir Putin -- in defiance of almost the entire international community.
"Today was the hardest, cruelest of the seven days of this war," said Vadym Boychenko, the mayor of the key southeastern port of Mariupol who said Russian forces pummeled the city for hours and were attempting to block civilians from leaving.
"Today they just wanted to destroy us all," he said in a video on Telegram, accusing Russian forces of shooting at residential buildings.
Boychenko said more of the city's vital infrastructure was damaged in the assault, leaving people without light, water or heating.
In Washington, top US diplomat Antony Blinken warned the human costs were already "staggering," accusing Russia of attacking places that "aren't military targets."
"Hundreds if not thousands of civilians have been killed or wounded," said the secretary of state, who will travel to eastern Europe next week to shore up support for Ukraine -- and for efforts to secure a ceasefire.
Kyiv is sending a delegation to the Thursday ceasefire talks, at an undisclosed location on the Belarus-Poland border, but has warned it would not accept "ultimatums."
At the United Nations, the General Assembly overwhelmingly adopted a resolution Wednesday that "demands" Russia "immediately" withdraw from Ukraine, in a powerful rebuke of Moscow by a vast majority of the world's nations.
After more than two days of extraordinary debate, which saw the Ukrainian envoy accuse Russia of genocide, 141 out of 193 member states backed the non-binding resolution -- with only Eritrea, North Korea, Syria and Belarus joining Russia against.
At least 350 civilians including 14 children have so far been killed, Ukrainian authorities say, and hundreds of thousands have fled the country since the invasion began, triggering punishing Western sanctions intended to cripple Russia's economy.
The UN rights office, OHCHR, said it had registered 752 civilian casualties including 227 deaths -- but believes the reality is "considerably higher."
"The humanitarian consequences will only grow in the days ahead," Blinken warned.
At the UN, the US ambassador echoed Blinken's alarm about mounting civilian deaths -- accusing Moscow of moving cluster munitions and other arms banned under international conventions into its neighbor.
"It appears Russia is preparing to increase the brutality of its campaign against Ukraine," Linda Thomas-Greenfield told the General Assembly.
Russia said Wednesday it had captured the Black Sea port of Kherson, population 290,000, though the claim was not confirmed by mayor Igor Nikolayev who appealed online for permission to transport the dead and wounded out of the city and for food and medicine to be allowed in.
"Without all this, the city will die," he wrote.
AFP witnessed the aftermath of apparent Russian bombing on a market and a residential area in Zhytomyr in central Ukraine, and in Kharkiv, Ukraine's second biggest city.
"There is nowhere in Kharkiv where shells have not yet struck," said Anton Gerashchenko, an adviser to Ukraine's interior minister, after Russian airborne troops landed in the city before dawn.
Shelling in the northeastern city of 1.4 million a day earlier drew comparisons to the massacres of civilians in Sarajevo in the 1990s.
'Erase us all'
As Russian artillery massed outside Kyiv, the former champion boxer turned city mayor Vitali Klitschko vowed to stand strong.
"The enemy is drawing up forces closer to the capital," he said. "Kyiv is holding and will hold. We are going to fight."
Residents have been hunkered down in Kyiv for a week and dozens of families were sheltering Wednesday in the Dorohozhychi metro station.
In a video address, Ukraine's President Volodymyr Zelensky said Russian forces wanted to "erase our country, erase us all".
Five people were killed in an attack a day earlier on the Kyiv television tower at Babi Yar, the site of a Nazi massacre in which over 33,000 people were killed -- most of them Jews.
The 44-year-old Zelensky, who is himself Jewish, urged Jewish people around the world to speak up.
"Nazism is born in silence. So, shout about killings of civilians. Shout about the murders of Ukrainians," he said.
New US sanctions
With the civilian toll mounting, opposition to the conflict is also growing within Russia.
Dozens of anti-war demonstrators were detained in Moscow and Saint Petersburg after jailed Kremlin critic Alexei Navalny called Russians to the streets, dismissing Putin as "an insane little tsar".
Internationally, meanwhile, the United States announced a new set of sanctions, this time targeting Russian ally Belarus and Russia's defense industry.
Authoritarian Belarus and Russia are closely linked and Belarus has been used as a key staging ground for the invasion of neighboring Ukraine.
Western countries have already imposed heavy sanctions on Russia's economy and there have been international bans and boycotts against Russia in everything from finance to tech, from sports to the arts.
In France, President Emmanuel Macron said in an address to the nation Europe had entered a "new era," and would need to both invest in its defenzes and wean itself off reliance on Russian gas.
EU and NATO members have already sent arms and ammunition to Ukraine, although they have made clear that they will not send troops and the EU has dampened Zelensky's hopes of membership of the bloc.
Chelsea for sale
In its latest move to isolate Russia, the European Union banned broadcasts of Russian state media RT and Sputnik and excluded seven Russian banks from the global SWIFT bank messaging system.
In London, meanwhile, Chelsea's Russian owner Roman Abramovich said he had made the "incredibly difficult" decision to sell the Premier League club, pledging proceeds would go to Ukraine war victims.
Abramovich, alleged to have close links to Putin, has not been named on a British sanctions list targeting Russian banks, businesses and pro-Kremlin tycoons.
But the Chelsea owner's concern about potential seizing of assets is understood to have sparked his move.