Ukrainian President Volodymyr Zelenskyy said in a Monday video address the port city of Mariupol is being "reduced to ashes" during its siege by Russia but assured it would "survive," CNN reported.

Zelenskyy also urged Ukrainian citizens to "do everything you can to defend our country, to save our people."

"We are seeing more and more heroes. Once ordinary Ukrainians, and now true fighters," he said.

The Ukrainian president added ordinary citizens were "rising" to the point that Russia "doesn't believe that this is the reality."

"We will make Russia believe," Zelenskyy emphasized. "Fight, keep on fighting, and help."

The remarks from Zelenskyy follow the rejection of an ultimatum Sunday from Russian officials that Ukrainian forces surrender the city, Reuters reported.

"There can be no question of any surrender" in Mariupol, Ukrainian deputy Prime Minister Iryna Vereshchuk said.

Mariupol Mayor Piotr Andryushchenko also rejected the offer in a Facebook post, according to Interfax Ukraine.

Ukrainian officials and non-profit organizations in Mariupol are saying food, water, and electricity are running low and outside communications are severed, CBS News reported.

However, some analysts still believe the war against attrition will catch up to Russia.

"The block-by-block fighting in Mariupol itself is costing the Russian military time, initiative, and combat power," the Institute for the Study of War said in an assessment Saturday.

"If and when Mariupol ultimately falls the Russian forces now besieging it may not be strong enough to change the course of the campaign dramatically by attacking to the west."

The city government has said at least 2,300 people have died due to the Russian siege, CBS News reported.

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