Russia is claiming to have captured the port in the heavily besieged city of Mariupol after showing footage of more than 1,000 Ukrainian marines giving themselves up.
Mariupol has been devastated by Russian shelling, leaving the city in rubble and there has been evidence to suggest war crimes have been committed with hospitals and train stations among the buildings hit.
Ukrainians have vowed to fight on in Mariupol with food and water dwindling in a city with strong strategic interest for Russia.
It has been heavily under siege since the start of the invasion on February 24 and Russia is now claiming to have taken the city's port with Ukrainian fighters running out of ammunition.
But the Ukraine government is so far denying that Mariupol's port has fallen.
Russian state television has shown what appears to be Ukrainian soldiers surrendering at a steelworks and walking with hands up.
Russia's defence ministry on Wednesday said 1,026 soldiers from Ukraine's 36th Marine Brigade, including 162 officers, had surrendered in Mariupol, which has been besieged for weeks, and that the port was fully under its control.
Capturing its Azovstal industrial district, where the marines have been holed up, would give the Russians full control of Ukraine's main Sea of Azov port, reinforce a southern land corridor and expand its occupation of the country's east.
Ukraine's general staff said Russian forces were attacking Azovstal and the port, but a defence ministry spokesman said he had no information about any surrender.
"Russian forces are increasing their activities on the southern and eastern fronts, attempting to avenge their defeats," Ukrainian President Volodymyr Zelensky said in a Wednesday night video address.
Reuters journalists accompanying Russian-backed separatists saw flames billowing from the Azovstal area on Tuesday, a day after Ukraine's 36th Marine Brigade said its troops had run out of ammunition.
Chechen leader Ramzan Kadyrov, an ardent supporter of Russian President Vladimir Putin, urged remaining Ukrainians trapped in Azovstal to surrender.
"Within Azovstal at the moment there are about 200 wounded who cannot receive any medical assistance," Kadyrov said in a Telegram post. "For them and all the rest it would be better to end this pointless resistance and go home to their families."
Ukraine says tens of thousands of people are believed to have been killed in Mariupol and accuses Russia of blocking aid convoys to civilians marooned there.
Its mayor, Vadym Boichenko, said Russia had brought in mobile crematoria "to get rid of evidence of war crimes."
Moscow has blamed Ukraine for civilian deaths and accused Kyiv of denigrating Russian armed forces.
