"There can be no talk of surrendering weapons. We have already informed the Russian side of this," Iryna Vereshchuk told Ukrainska Pravda newspaper.

"It's a deliberate manipulation and it's a real hostage situation," she added of the demand.

Russia gave the city an ultimatum late Sunday, urging its defenders to surrender before 05:00 am on Monday.

"We call on units of the Armed Forces of Ukraine, territorial defence battalions, foreign mercenaries to stop hostilities, lay down their arms and, along the humanitarian corridors agreed with the Ukrainian side, enter the territories controlled by Kyiv," said Mikhail Mizintsev, head of the Russian National Defence Control Centre.

The Russian defence ministry, addressing Mariupol authorities on messaging app Telegram, wrote: "You are the ones who now have the right to make a historic choice -- either you are with your people or you are with the criminals.

"Otherwise, the court martial that awaits you is only a little of what you have already earned because of your despicable attitude toward your own citizens, as well as the horrible crimes and provocations you have committed."

Mariupol, a strategic, mostly Russian-speaking port in the southeast, has been one of the main targets of Moscow's attacks.

The city has been hammered by Russian shelling for days, has seen a near-total communications blackout and is cut off from food, water and other supplies. 

'Kidnapped children'

The Russian defence ministry had said it would open humanitarian corridors to allow residents to leave by 10:00 am if the surrender was agreed. 

It said it had "comfortable buses" waiting at checkpoints to transport refugees to various destinations, and that all those arriving in Russia would get three hot meals a day and round the clock medical assistance.

Almost 60,000 "rescued residents of Mariupol" were already in Russia, it said, "now openly talking about all the mass atrocities and crimes committed" by the Mariupol authorities.

But in a video on Telegram, Vereshchuk said the Russians "continue to behave like terrorists".

"They say they agree on the humanitarian corridor and in the morning, shell the place for evacuation," she said.

Mariupol officials have said occupying soldiers have also forcibly transported around a thousand residents to Russia and stripped them of their Ukrainian passports -- a possible war crime.

In Vereshchuk's comments to Ukrainska Pravda, she said children were being "kidnapped" from orphanages. 

"To understand: 350 children are going to be forcibly taken to Russia without allowing us to get them," she said. 

"We ask clearly: give us a corridor and write which orphanage they are going to and why. They immediately took those children to Russia. This is terrorism."