The port city of Kherson in Ukraine's south has reportedly become the first major city in the country to be taken over by Russian forces.
It came as Volodymyr Zelenskyy, in an overnight video address, called on Ukrainians to keep up the resistance.
"They will have no peace here. They will have no food. They will have here not one quiet moment."
Moscow's isolation deepened, meanwhile, when most of the world lined up against it at the United Nations to demand it withdraw from Ukraine.
After seven days of Russian assault, the UN's refugee agency announced that 1 million people had fled Ukraine since the invasion, the swiftest exodus of refugees this century.
Other recent developments on the ground in Ukraine include:
- Russian officials arrived in Belarus ahead of peace talks on Thursday
- Russian forces reportedly surrounded the coastal city of Mariupol
- Shelling and air strikes continued in Kharkiv
- An explosion rocked a Kyiv railway station
- Russia and Ukraine gave conflicting casualty figures
Russian forces in 'complete control' of Kherson
Kherson's mayor, Igor Kolykhayev, told Reuters on Wednesday night (local time) that Russian troops were in the streets and had forced their way into the city council building.
Ukraine's government had earlier played down reports that Kherson, a strategically important shipbuilding city of 280,000 on the banks of the Dnieper River near where it flows into the Black Sea, had fallen into Russian hands.
Mr Kolykhayev urged Russian soldiers not to shoot at civilians and publicly called on civilians to walk through the streets only in daylight and in ones and twos.
"We do not have the armed forces in the city, only civilians and people who want to live here!" he said in a statement.
The New York Times reported that a senior Ukrainian government official had confirmed that Russian troops had seized the city.
However, Mr Zelenskyy's office told The Associated Press that it could not comment on the situation in Kherson while the fighting was still going on.
Russian Defence Ministry spokesman Igor Konashenkov said Kherson was under Russia's "complete control".
He said the city's civilian infrastructure, essential facilities and transport were operating as usual and there were no shortages of food or essential goods.
Mr Konashenkov said talks between the Russian commanders, city administrations and regional authorities on how to maintain order in the city were underway on Wednesday (local time).
A senior US defence official said that they had seen claims that the Russians had taken Kherson, but that the Ukrainian military was rejecting that claim.
"Our view is that Kherson is very much a contested city at this point," said the official, who spoke on the condition of anonymity to make military assessments.
In his video address early on Thursday morning (local time), Mr Zelenskyy did not comment on whether the Russians had seized several cities, including Kherson.
"If they went somewhere, then only temporarily. We'll drive them out," he said.
He said the fighting was taking a toll on the morale of Russian soldiers, who "go into grocery stores and try to find something to eat".
"These are not warriors of a superpower," he said. "These are confused children who have been used."
He said the Russian death toll has reached nearly 9,000.
"Ukraine doesn't want to be covered in bodies of soldiers," he said. "Go home."
Peace talks due on Thursday
Earlier, an aide to Russian President Vladimir Putin told reporters the Ukrainians were expected to arrive in Belarus to resume talks on Thursday.
"As far as I understand, the Ukrainian delegation has already left Kyiv and is currently in transit," Vladimir Medinsky told reporters in the south-western Belarusian city of Brest.
"We understand the logistic difficulties for them," he said, adding that Belarus guaranteed the safety of the Ukrainian side in Belarus, and Russia's military had created a safe corridor for their passage through Ukraine.
Mr Medinsky said th sides had "reached a mutual understanding on several proposals at the negotiating table" at the first round of talks on a potential ceasefire in Belarus on Monday.
Mr Zelenskyy has said Russia must stop bombing if it wants to negotiate.
The US accused Russia of launching a "full war on media freedom and the truth" by blocking independent news outlets and preventing Russians from hearing news of the invasion of Ukraine.
"Russia's government is also throttling Twitter, Facebook, and Instagram platforms that tens of millions of Russia's citizens rely on to access independent information and opinions," the State Department said in a statement.
Coastal city of Mariupol encircled
Earlier, Britain's Defence Ministry said Mariupol, a large port city further east from Kherson on the Azov Sea, was encircled by Russian forces.
Mariupol Mayor Vadym Boychenko said the attacks there had been relentless.
"We cannot even take the wounded from the streets, from houses and apartments today, since the shelling does not stop," he was quoted by the Interfax news agency as saying.
Russian pounding of Kharkiv continues
Russia has continued bombing Kharkiv, Ukraine's second-largest city with about 1.5 million inhabitants.
Another round of aerial attacks shattered buildings and lit up the skyline with balls of fire on Wednesday.
At least 21 people were killed and 112 injured over the past day, said Oleg Sinehubov, head of the Kharkiv regional administration.
A member of the Organisation for Security and Cooperation (OSCE) in Europe's special Ukraine monitoring mission was killed during the shelling on Kharkiv on Tuesday, the OSCE said in a statement on Wednesday.
The OSCE named the victim as Maryna Fenina, and said she had died "while getting supplies for her family in a city that has become a war zone".
In the city of Izyum, around 120km south-east of Kharkiv, Russian shelling killed six adults and two children, Ukraine's parliament said.
Several Russian planes were shot down over Kharkiv, according to Oleksiy Arestovich, a top adviser to Ukrainian President Volodymyr Zelenskyy.
"Kharkiv today is the Stalingrad of the 21st century," Mr Arestovich said, invoking what is considered one of the most heroic episodes in Russian history, the five-month defence of the city from the Nazis during World War II.
From his basement bunker, Kharkiv Mayor Igor Terekhov told the BBC: "The city is united and we shall stand fast.''
Russian attacks, many with missiles, blew the roof off Kharkiv's five-storey regional police building and set the top floor on fire, and also hit the intelligence headquarters and a university building
Officials said residential buildings were also hit, but gave no details.
Explosion rocks Kyiv train station
Russia's 64-kilometre-long convoy of tanks and other vehicles remained outside the capital, Kyiv, which continued to be struck by shelling.
An explosion hit near Kyiv's central train station where thousands of women and children were being evacuated on Wednesday evening.
Interior Ministry adviser Anton Herashchenko said in an online post said it was caused by falling wreckage from a Russian missile shot down by Ukrainian air defence.
The falling debris hit a heating pipe, causing the blast, but caused far less damage and casualties than if the missile had hit its target in central Kyiv, he said, without saying if anyone had been hurt in the explosion.
On the far edges of Kyiv, volunteer fighters well into their 60s manned a checkpoint to try to block the Russian advance.
"In my old age I had to take up arms," said Andrey Goncharuk, 68. He said the fighters needed more weapons, but "we'll kill the enemy and take their weapons."
Russian warplanes bombed the village of Gorenka, a half-hour's drive from Ukraine's capital, on Wednesday, leaving the bodies of villagers strewn among ruined homes, residents said.
In the aftermath, Larissa Lipatova crowded under blankets with seven other villages in a cold, damp concrete cellar among jars of pickled vegetables.
A candle stuck in a pickle jar, propped up in front of a religious icon, provided their only light.
Ms Lipatova wept, covering her face with one hand, as she spoke in the dark with a message for Ukraine's invaders.
"We don't need to be freed. Leave us alone!"
Gorenka resident Pjotr Vyerko, an 81-year-old French teacher, said he was prepared to use his rifle to shoot invaders because he had a daughter and grandson.
As Russia intensifies its bombardment of cities, streams of refugees have been pouring out of the country, most crossing into Poland and Romania.
The UN's refugee agency estimates up to 4 million people could try to flee the Russian invasion.
The majority are expected to stay in Europe but Australian organisations have already received a large number of requests for help.
The federal government has approved 1,000 visas for Ukrainians displaced by the Russian invasion, with several people due to arrive in Australia this weekend.
The majority will come on temporary visas.
"The government is progressing visa applications from Ukrainian nationals as a priority," Immigration Minister Alex Hawke said.
Conflicting casualty figures
The UN Human Rights Office said it had confirmed the deaths of 227 civilians and 525 injuries during the conflict as of midnight on March 1, mostly caused by "the use of explosive weapons with a wide impact area".
It cautioned that the real toll would be much higher due to reporting delays.
Russia's Defence Ministry said 498 Russian soldiers had died and another 1,597 had been wounded since the start of the invasion, the first time Moscow put a figure on its casualties.
It said more than 2,870 Ukrainian soldiers and "nationalists" had been killed, Interfax news agency reported.
Ukraine said almost 9,000 Russian soldiers had been killed so far and hundreds taken prisoner, and while it did not report its own military losses, it said 2,000 Ukrainian civilians had died.
The numbers given by Moscow and Kyiv could not be independently verified.
ABC/Wires
