Russia's defence ministry has told the Ukrainian forces still fighting in the besieged southern port of Mariupol to lay down their arms within hours in order to save their lives.
Russia's earlier claim that its troops had cleared the urban area of Mariupol, scene of the war's heaviest fighting and worst humanitarian catastrophe, could not be independently verified. It would be the first major city to have fallen to Russian forces since the 24 February invasion.
Moscow says the remaining fighters in Mariupol - who it says are both Ukrainian and foreign - are blockaded in the Azovstal steelworks plant, giving them until 0300 GMT (1300 AEST) on Sunday to surrender.
"Taking into account the catastrophic situation that has developed at the Azovstal metallurgical plant, as well as being guided by purely humane principles, the Russian Armed Forces offer the militants of nationalist battalions and foreign mercenaries from 06:00 (Moscow time) on April 17, 2022, to stop any hostilities and lay down their arms," the defence ministry said in a statement.
"All who lay down their arms are guaranteed that their lives will be spared."
Under the terms of a deal proposed by Russia on Saturday, the remaining defenders in the Azovstal plant would leave between 6am and 1pm Moscow time, without weapons or ammunition.
The start of the surrender would be indicated by raising flags, the ministry said: "From the Russian side - red; from the Ukrainian side - white, around the whole perimeter of Azovstal."
There was no immediate reaction from Kyiv to the offer.
Earlier, President Volodymyr Zelenskyy told the Ukrainska Pravda news portal that the situation is "very difficult" in Mariupol.
"Our soldiers are blocked, the wounded are blocked. There is a humanitarian crisis ... Nevertheless, the guys are defending themselves," he said.
As Russia launched more long-range attacks following the sinking of its Black Sea fleet's flagship, Moscow said its warplanes had struck a tank repair factory in Kyiv. 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.
The Ukrainian military said Russian warplanes that took off from Belarus had fired missiles at the Lviv region near the Polish border and four cruise missiles were shot down by Ukrainian air defences.
The western city has been relatively unscathed so far and serves as a haven for refugees and international aid agencies.
Reuters journalists in Russian-held districts reached the Ilyich steelworks in mariupol, one of two metals plants where defenders have held out in underground tunnels and bunkers. Moscow claimed to have captured it on Friday.
The factory was reduced to a ruin of twisted steel and blasted concrete, with no sign of defenders present. Several bodies of civilians lay scattered on nearby streets, including a woman in a pink parka and white shoes.
Someone had spraypainted "mined" on a fence by an obliterated filling station. In a rare sign of life, one red car drove slowly down an otherwise empty street, the word "children" scrawled on a card taped to the windshield.
A burned out tank is pictured outside the Azovmash research and manufacturing complex in Mariupol on 16 April, 2022. Source: AAP / TASS/Sipa USA
The governor of Kharkiv province in the east said at least one person had been killed and 18 were injured in a missile strike.
Smoke billowed from burning cars and the remains of what appeared to be an office building at the scene of an attack in the city as rescuers cleared mounds of debris that blocked the road outside.
In Mykolaiv, a city close to the southern front, Russia said it had struck a military vehicle repair factory.
The attacks followed Russia's announcement on Friday that 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.
Kyiv and Washington say the ship, whose sinking has become a symbol of Ukrainian defiance, was hit by Ukrainian missiles. Moscow says it sank after a fire and that its crew of around 500 were evacuated.
Russia's Defence Ministry published video of the head of the navy, Admiral Nikolai Yevmenov, meeting on a parade ground with about a hundred sailors it said were members of the crew.
A month and a half into President Vladimir Putin's invasion of Ukraine, Russia is trying to capture territory in the south and east after withdrawing from the north following an assault on Kyiv that was repelled at the capital's outskirts.
Russian troops that pulled out of the north left behind towns littered with bodies of civilians, evidence of what US President Joe Biden this week called genocide - an attempt to erase Ukrainian national identity.
Russia denies targeting civilians and says the aim of its "special military operation" is to disarm its neighbour, defeat nationalists and protect separatists in the southeast.
'Mariupol will always be Ukraine'
If Mariupol falls it would be Russia's biggest prize of the war so far. It is the main port of the Donbas, a region of two provinces in the southeast which Moscow demands be fully ceded to separatists.
The owner of both of the giant steelworks in Mariupol, Ukraine's richest man Rinat Akhmetov, vowed to rebuild the city. "Mariupol has been and will always be a Ukrainian city," Mr Akhmetov told Reuters.
Ukraine says it has so far held off Russian advances elsewhere in the Donbas regions of Donetsk and Luhansk, where at least one person was killed in shelling overnight.
In the front-line Luhansk town of Lysychansk, civilians crouched and then fled for safety from incoming shells as thick smoke rose from a blackened shop and burned-out cars.
Servicemen of the Donetsk People's Republic people's militia are seen in the Levoberezhny District of Mariupol. Source: Getty / TASS/Sipa USA
But Mr Putin appears determined to capture more Donbas territory to claim victory in a war that has left Russia subject to increasingly punitive Western sanctions and with few allies.
Mr Zelenskyy told Ukrainian reporters the world should prepare "in a number of ways" for the possibility Russia might use nuclear weapons. He did not give evidence for the assertion.
Last month, Kremlin spokesman Dmitry Peskov said Russia would resort to nuclear weapons only in the case of a "threat to the existence" of the country - and not as a result of the Ukraine conflict. read more
An advisor to Mr Zelenskyy said the country needed a swifter supply of weapons from its European Union partners.
"Ukraine needs weapons. Not in a month. Now," Mykhailo Podolyak said in a Twitter post.
The Russian defence ministry said its anti-aircraft systems in the Odesa region shot down a Ukrainian transport plane delivering weapons supplied by Western governments. It did not provide any evidence. There was no immediate comment from Kyiv.
Mr Zelenskyy said about 2,500-3,000 Ukrainian troops have been killed so far and up to 20,000 Russian troops.
Moscow has given no updates on its casualties since 25 March, when it said 1,351 had died. Western estimates of Russian losses are many times higher, while there are few independent estimates of Ukraine's losses.
Ukraine says civilian deaths are impossible to count, estimating at least 20,000 killed in Mariupol alone.
Overall, around a quarter of Ukrainians have been driven from their homes, including a tenth of the population that has fled abroad.
