Russian paratroopers stormed a military hospital in the Ukrainian city of Kharkiv overnight.
It comes as soldiers close in on Kyiv, with a convoy of Russian military vehicles now 20 miles northwest of the capital.
The paras launched the attack on the hospital in the early hours of this morning with prolonged fighting throughout the night.
The region's Police Chief Volodymyr Tymoshko said no Ukrainian troops were killed in the gunfight.
He said: "Currently the situation near the hospital is under control, security has been strengthened."
Ukraine's south-eastern port of Mariupol was also under constant shelling from Russia and unable to evacuate the injured while Kherson, on the Black Sea to the west, was completely surrounded by invading forces, Ukrainian authorities said on Wednesday.
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Meanwhile rocket strikes on the centre of Kharkiv have killed at least 21 people.
Kyiv's mayor published a video showing the moment when a tall TV antennae in the city was engulfed in flames, apparently hit by a rocket.
"We are fighting, we are not ceasing to defend our motherland," Mariupol mayor Vadym Boichenko said live on Ukrainian TV.
West of Kyiv, in the city of Zhytomyr, four people, including a child, were killed on Tuesday by a Russian cruise missile, a Ukrainian official said.
Elsewhere, rocket strikes on the centre of Kharkiv killed at least 21 people, regional governor Oleg Synegubov said.
Similar strikes that killed and wounded dozens in Kharkiv the previous day involved cluster bombs, experts said.
Ukrainian President Volodymyr Zelensky said Russia must stop bombing Ukrainian cities before meaningful talks on a ceasefire could start, as a first round of negotiations this week had yielded scant progress.
"It's necessary to at least stop bombing people, just stop the bombing and then sit down at the negotiating table," he said.
Defence Secretary Ben Wallace warned that Russia would use indiscriminate carpet bombing tactics against Ukrainian cities.
He told Sky News that Russian advances were being hampered by resistance they had seen "footage of Ukrainians using UAVs to attack petrol train convoys, to go after logistical lines, we have seen railway lines blown up" but there had also been a switch in Moscow's tactics as a result.
"What you are seeing now is those heavy bombardments at night, they won't come into the cities as much, they will - I'm afraid, as we have seen tragically by the looks of things - carpet-bomb cities, indiscriminately in some cases."
