Russia said its troops have taken control of the entire city of Mariupol and only a small contingent of Ukrainian soldiers remained inside a steel factory in the key southern port on Saturday.
The Russian defence ministry said its troops had "completely cleared" Mariupol's urban area of Ukrainian forces and blockaded the "remnants" in the Azovstal steelworks. The Ukrainian forces in the city had lost more than 4,000 personnel, RIA news agency reported.
The besieged city has seen fierce fighting since the war began and its capture has been a key objective of the Russian forces as the strategic port provides the breakaway Donbas region and Russia a land route to the Black Sea.
Russia's Defence Ministry said if Ukrainian forces in the Azovstal steelworks lay down their arms starting at 0300 GMT on Sunday, their lives would be spared, Tass news agency reported.
A senior Russian officer was quoted as saying the offer was prompted by "the catastrophic situation in the steelworks as well as purely humane principles".
"The situation is very difficult" in Mariupol, President Volodymyr Zelenskiy told the Ukrainska Pravda news portal. "Our soldiers are blocked, the wounded are blocked. There is a humanitarian crisis … Nevertheless, the guys are defending themselves," according to a Reuters report from Kyiv.
Reuters said that two of its journalists reached the Ilyich steelworks in Mariupol, one of two steel plants where Ukraine's soldiers had held out in underground tunnels and bunkers. Russian troops had captured the site on Friday.
The factory was reduced to a ruin of twisted steel and blasted concrete, with no sign of defenders present.
Russian forces also launched long-range missile attacks across the country following the sinking of its Black Sea flagship, Moscow said its warplanes had struck a tank repair factory in Kyiv on Saturday.
An explosion was heard and smoke rose over the southeastern Darnytskyi district. The mayor said at least one person was killed and medics were fighting to save others.
Russian fighter jets that took off from Belarus had fired missiles at the Lviv region near the border with Poland.
In Mykolaiv, a city close to the southern front, Russia said it had destroyed a military vehicle repair factory.
The stepped up military action comes after Russia's announcement on Friday it would intensify long-range strikes in retaliation for unspecified acts of "sabotage" and "terrorism", hours after it confirmed the sinking of its Black Sea flagship, the Moskva.