Russian forces have seized Kherson in southern Ukraine, the city's mayor has said, as he issued a desperate appeal for food and medicine to be allowed in.
Igor Kolykhaiev, who also appealed to Russia for permission to transport the dead and wounded out from the port city, said on Facebook: "Without all this, the city will die."
It would make it the first, and biggest, city to fall yet in the invasion.
The development came as the UN refugee agency said one million people have fled Ukraine since Russia's invasion, in the swiftest exodus of refugees this century.
Mr Kolykhaiev said Vladimir Putin's soldiers had forced their way into the city council building and enforced a curfew on residents.
He said he has asked them not to shoot civilians, and to allow crews to gather up bodies from the streets.
However, a senior US defence official disputed Russia has complete control of the city.
And the UK Ministry of Defence said in an intelligence update on Thursday 'the military situation remained unclear'.
"I simply asked them not to shoot at people," Mr Kolykhaiev said in a statement.
"We don't have any Ukrainian forces in the city, only civilians and people here who want to live."
The US countered the claim, with an official saying: "Our view is that Kherson is very much a contested city."
The MOD said: "Some Russian forces have entered the city of Kherson but the military situation remains unclear."
Images emerging from the city appear to confirm that.
CCTV footage has been revealed showing Russian combat vehicles and tanks on the central square of Kherson, as Moscow claimed the city had fallen as the first conquered in the invasion.
Kherson, a Black Sea shipbuilding city, has a population of around 280,000.
The BBC reported Mr Kolykhaiev called on residents to follow conditions set by Russian forces in order to 'keep the Ukrainian flag flying'.
"The (Russian) occupiers are in all parts of the city and are very dangerous," Gennady Lakhuta, head of the regional administration, was quoted as saying by AFP news agency.
The MOD said Mariupol, a large port city on the Azov Sea, was encircled by Russian forces, as reports of explosions rocking Kyiv and Kharkiv overnight emerged.
The Ukrainian Parliament, meanwhile, said a Russian bombing attack on Izium began just before midnight.
They said six adults and two children were found dead after a building was shelled by Russia.
UK defence chiefs said a Russian military convoy advancing on Kyiv remained 30km away from the capital.
It's been delayed by 'staunch resistance, mechanical breakdown and congestion', the Ministry of Defence said in the morning update.
"The column has made little discernible progress in over three days."
The cities of Kharkiv, Chernihiv and Mariupol 'remain in Ukrainian hands, added the MOD.
