Ukrainian President Volodymyr Zelensky has accused Russia of wanting to "destroy" the entire eastern region of Donbas, as the last remaining forces in the strategic port of Mariupol prepared Monday for a final defence.
Moscow is pushing for victory in the southern city as it works to wrest control of Donbas and create a land corridor to already-annexed Crimea.
Ukraine has pledged to fight on and defend the city, defying a Russian ultimatum on Sunday that called on the remaining fighters inside the encircled Azovstal steel plant to lay down their arms and surrender.
The Ukrainian authorities have urged people in Donbas to move west to escape a large-scale Russian offensive to capture the regions of Donetsk and Lugansk.
"Russian troops are preparing for an offensive operation in the east of our country in the near future. They want to literally finish off and destroy Donbas," Zelensky said in a statement.
Mariupol has become a symbol of Ukraine's unexpectedly fierce resistance since Russian troops invaded the former Soviet state on 24 February.
"The city still has not fallen," Prime Minister Denys Shmyhal said.
"There's still our military forces, our soldiers. So they will fight to the end. We will not surrender."
While several large cities were under siege, only Kherson in the south has fallen under Russian control, and more than 900 towns and cities have been re-captured.
Thousands of civilians facing famine
The UN World Food Programme says that more than 100,000 civilians in Mariupol are on the verge of famine and lack water and heating.
Ukraine's Minister of Digital Transformation Mykhailo Fedorov said the city was on "the verge of a humanitarian catastrophe", saying there was compelling evidence of Russian atrocities there.
"We will hand everything over to The Hague. There will be no impunity."
The mayor of Bucha -- a town near Kyiv where the discovery of dead civilians sparked international condemnation and war crimes accusations -- said Russian troops had raped men as well as women and children there.
Zelensky invites Macron to 'see for himself'
Zelensky said he had invited his French counterpart to visit Ukraine to see for himself evidence that Russian forces have committed "genocide" -- a term President Emmanuel Macron has avoided.
"I talked to him yesterday," Zelensky told CNN in an interview recorded on Friday but broadcast Sunday.
"I just told him I want him to understand that this is not war, but nothing other than genocide. I invited him to come when he will have the opportunity. He'll come and see, and I'm sure he will understand."
Zelensky, describing the situation in Mariupol as "inhuman", has called on the West to provide heavy weapons.
Russia has warned the United States this week of "unpredictable consequences" if it sent its "most sensitive" weapons systems to Ukraine.
