Ukraine warned on Wednesday that Russia was ramping up efforts in the South and East as it seeks full control of Mariupol, in what would be the first major city to fall, while Western governments committed more military help to bolster Kyiv.
The Kremlin's nearly seven-week-long incursion, the biggest attack on a European state since 1945, has not gone to plan.
Russia has been forced to pull back from some northern areas even as attacks across the country have turned Ukrainian cities to rubble and caused more than 4.6 million people to flee abroad.
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. read more
"Russian forces are increasing their activities on the southern and eastern fronts, attempting to avenge their defeats," Ukrainian President Volodymyr Zelenskiy 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.