At least 300 people were killed in a theater bombing in the Ukrainian city of Mariupol last week.
The number is said to have come from the people who were inside the building at the time.
It became “the last refuge for hundreds of innocent people”, the council said in a statement.
Elsewhere, the city of Chernihiv is now cut off by the Russian military, its governor has said.
Regional police said four people were killed in Russian shelling on a clinic providing humanitarian aid in the eastern city of Kharkiv.
Mayor Volodymyr Borisenko said in the city of Boryspil, southeast of Kyiv, and close to an international airport, about 20,000 people have responded to the appeal to leave.
Meanwhile, the United States is to supply more liquefied natural gas to the European Union to help reduce its reliance on supplies from Russia, which President Joe Biden has described as a “joint game plan.”
“This initiative focuses on two main issues – one helping Europe reduce its reliance on Russian gas as quickly as possible and the other, reducing Europe’s gas demand as a whole,” he said.
Mr Biden is visiting Poland this afternoon – home to more than two million Ukrainian refugees – after warnings that NATO will respond “in kind” if Russia uses chemical weapons.
The refugee crisis will be one of the key issues as he will meet the President of Poland, while he will also visit US troops stationed in Rzczów, near the border with Ukraine.
Earlier, he has met European Commission President Ursula von der Leyen in Brussels, which hosted a summit. NATO and G7 leaders in Brussels on Thursday,
It was there that the US leader called Russian President Vladimir Putin “brutal” and said that any chemical attack would “respond in kind” – but NATO would “make that decision at that time”.
“The nature of the response will depend on the nature of the use,” Biden said.
Ukraine news live: NATO will provide four more battle groups in Eastern Europe
Fears are growing that Mr Putin may use chemical weapons to accelerate Russian military gains, which experts say are slower than expected.
Prime Minister Boris Johnson was also at the NATO meeting and warned of “very, very serious” consequences if Russia used chemical or biological weapons.
NATO has repeatedly insisted that it will not send any coalition troops to Ukraine.
In other developments:
, Russia’s deputy UN ambassador says it would use nuclear weapons if ‘provoked’
• Chelsea boss Roman Abramovich played early role in peace talks, claims Kremlin
• At least 1,035 Ukrainians have been killed and 1,650 injured, the UN says; but the actual number is likely to be much higher
PM denies Kremlin’s claim of being ‘anti-Russian’
Mr Johnson also hit back at comments that appeared to single out him as Russia’s most hated leader.
According to state news agency RIA, Kremlin spokesman Dmitry Peskov called the prime minister “the most active participant in the race to be anti-Russian”.
Mr Johnson told reporters he was “not remotely anti-Russian” and that no one involved in the international talks was against the Russian people.
Another 6,000 missiles to be sent to Ukraine In addition to the 4,000 already supplied, Mr Johnson disclosed on Thursday.
Read more: Light unlikely as families flee Ukraine’s most devastated city
Security forces imposed more sanctions as NATO
NATO, meanwhile, is bolstering defense in Eastern Europe with four new battle groups in Hungary, Romania, Bulgaria and Slovakia.
Sanctions are also intensifying, with the UK, US, Australia and Japan issuing an expanded list.
Britain’s Foreign Secretary Liz Truss said the Wagner group of Russian mercenaries – believed to have been tasked with assassinating Ukraine’s President Volodymyr Zelensky – was one of its 65 new targets,
US claims high failure rate on Russian missiles
The war – which the Kremlin calls a “special military operation” – has seen brutal civilian shelling in several cities, such as Mariupol in the south, where thousands hide in basements with no electricity and little food and water.
However, progress around the capital Kyiv appears to have stalled in recent weeks and no major cities have been captured.
The failure rate of some of Russia’s precision-guided missiles is reportedly as high as 60% – and it is now running out of weapons, according to US officials, speaking anonymously to the Reuters news agency.
Ukrainian officials claim that Russia has lost “15,800 personnel”, but NATO estimates it to be between 7,000 and 15,000 Russian deaths.
Ukraine’s growing successful counterattack
Buoyed by an influx of weapons from the West, Ukraine has also had some notable success in its counterattack.
Pictures appear to show a Russian landing ship caught fire near BardianskyWhich was confiscated on 27 February.
Despite slow progress, Ukrainian military officials said on Thursday that Russia was attempting to resume efforts to capture Mariupol, as well as Chernihiv, Sumy, Kharkiv and Kyiv.
According to Ukraine’s deputy PM, the “first full” exchange of POWs has also taken place.
Irina Vereshchuk said 11 Russian civilian sailors were handed back after being rescued from a sunken ship near the port city of Odessa.
In return, 19 Ukrainian civilian sailors are said to have returned home after their ship was captured.
Zelensky: Western aid came ‘a little late’
President Volodymyr Zelensky marked a month of war in his latest video message late last night.
“30th day. It’s been a month! If Russia knew it would face it, I’m sure they would certainly be afraid to come here,” he said.
Fighting continues, despite both sides saying that peace talks are progressing, and Mr Zelensky says a face-off with Mr Putin is needed to end the bloodshed.
The president previously thanked the West for “strong steps” on sanctions, but told leaders at the Brussels summit “it was a little late”.
“Because if it were deterrent, Russia would not have started the war,” he told them via video link.
Mr Zelensky did not put forth his demand for a no-fly zone, but instead asked for “1% of all your planes, 1% of all your tanks” – a request Boris Johnson later logically described as “very difficult”. .
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However, Western countries are said to be providing anti-ship weapons amid fears that Russia will launch amphibious attacks on the country’s Black Sea coast.
There have been some fierce attacks in the region, with Russia believed to be trying to establish a land corridor to Crimea and rebel-controlled areas in the east.