Defenders of the besieged city of Mariupol will fight to the end against Russian forces, Ukrainian Prime Minister Denys Shmyhal says.
The port city has not fallen despite an ultimatum from Moscow to remaining fighters to give up, he said.
Ukraine’s Foreign Minister Dmytro Kuleba said Russia has chosen to raze Mariupol to the ground.
Local officials said Russian forces have announced they will stop anyone from entering or leaving the city.
Capturing the whole of the city is seen as a major strategic prize for Russia, leaving it in control of a vast swathe of southern and eastern Ukraine.
An advisor to the mayor of Mariupol said residents would be forced to queue for a pass to enable them to move between districts and some could have their phones confiscated or be taken against their will to Russia.
In an interview with the US network ABC, Mr Shmyhal said a Russian deadline for Ukrainian forces in Mariupol to surrender by Sunday had been ignored.
“The city still has not fallen,” he said. “There is still our military forces, our soldiers, so they will fight until the end. And as for now, they still are in Mariupol.”
Russia’s military says it controls almost all of Mariupol, while Ukraine’s Azov Battalion is still holding out in Azovstal, a huge steelworks overlooking the Azov Sea.
Justin Crump, a military expert at security consultancy Sybilline, told the BBC there could be 500-800 Ukrainian troops holding out in the city.
“[The steelworks] has nuclear bunkers, tunnels, it’s built to survive a nuclear conflict – they are really well set for defence,” he said.
“They have had more than 50 days to fortify it and build escape routes,” Mr Crump added. “I suspect that unless they are wiped out they’ll be there a long time. It’s credible there would be guerrilla resistance.”
Ukraine has demanded that Russian forces open humanitarian corridors from Mariupol to allow civilians and wounded Ukrainian troops to leave, but no large-scale evacuations have taken place for several weeks.
The situation for civilians in the city is desperate, with homes destroyed and widespread water shortages.
As Mariupol defenders continue to hold out, Ukrainian officials still deny any possibility of territorial concessions to Russia.
In an interview broadcast on Sunday by CNN, President Volodymyr Zelensky brushed aside the idea of letting Moscow take over parts of eastern Ukraine to stop the conflict.
“Ukraine and its people are clear. We have no claim to anyone else’s territories but we are not going to give up ours,” he said.
Meanwhile, authorities in the western city of Lviv said six people were killed in rocket strikes on Monday morning.
It is not yet clear what the strikes were targeting. In recent weeks, Russia has focused its offensive on eastern Ukraine.