The proclaimed wins in the southern region of Kherson are the latest in a series of Russian defeats undermining the Kremlin's claim to have annexed around 20 percent of Ukraine.
Russian missiles early on Thursday struck the central city of Zaporizhzhia, killing several civilians, as rescue workers clawed through rubble with their bare hands searching for survivors, AFP journalists saw.
"The Armed Forces of Ukraine have liberated more than 400 square kilometres of the Kherson region since the beginning of October," southern army command spokeswoman Natalia Gumeniuk said in a briefing online.
She said that the recaptured territory was home to nearly 30 towns and villages that had been occupied by Russian forces for months.
Kherson, a region with an estimated pre-war population of around one million people, was captured early and easily by Moscow's troops after their invasion launched February 24.
Russian-installed officials have renewed a call for residents to remain calm, with deputy pro-Moscow leader Kirill Stremousov saying Kremlin forces were holding back the advance.
Addressing a meeting in Prague of European heads of state, President Volodymyr Zelensky called on Western capitals to supply his army with more weapons "to punish the aggressor".
He said Ukraine must fend off Moscow's invasion "so that Russian tanks do not advance on Warsaw or again on Prague".
The EU imposed its latest round of sanctions on Russia, expanding bans on trade and individuals over Moscow's formal annexation last Friday of four Ukrainian regions.
On Thursday, seven Russian missiles struck downtown Zaporizhzhia just 40 kilometres (25 miles) from the artillery battles of the southern front.
A woman, whose body was carefully removed from the rubble by rescuers, looked as though she had been asleep in bed when the building around her was destroyed.
"For the first time in my life, I feel pure hatred," said Igor Osolodko, a 25-year-old musician, one of dozens of volunteer rescuers.
"It's absurd, it's unreal. We need to rely on our army and cope with this terror until it's all over, until we win," he said.
Ukraine's military has also said it is reclaiming territory in the eastern Lugansk and Donetsk regions, that have been partially controlled by Kremlin proxies since 2014.
Ukrainian forces have made gains on the west bank of the river Dnieper that cuts through Kherson, but the Russian military in a briefing said Thursday that its forces rebuffed "repeated attempts to break through our defences" in the area.
Further west, on Ukraine's contact line with Russian forces from the Mykolaiv region -- where Kyiv's forces had been hunched in fox holes for months and pounded by Russian artillery -- the mood was shifting along with frontlines.
'End of the tunnel'
Bogdan, 29, from northwest Ukraine who re-enlisted in the military this year, has spent most of the summer holding the line in Mykolaiv some four kilometres from the Russians.
"We see their successes and it inspires us," he said of Ukrainian wins elsewhere in the country.
"If some thought before that we weren't moving fast enough, well now that's not the case!"
"There is light at the end of the tunnel," agreed commander Yaroslav, a sturdy 39-year-old man wearing a black cap.
The Ukrainian push deeper into Kherson is putting further strain on the Kremlin's announcement last week that it had annexed the territory -- alongside three others -- and that its residents were would Russian "forever".
The four territories -- Donetsk, Kherson, Lugansk and Zaporizhzhia -- create a land corridor between Russia and the Crimean peninsula, which was annexed by Moscow in 2014.
Together, the five regions make up around 20 percent of Ukraine.
Ukrainian Foreign Minister Dmytro Kuleba accused Russian forces of "deliberately striking civilians to sow fear".
"Russian terror must be stopped -- by force of weapons, sanctions and full isolation", he said.
In Russia, opposition figure Vladimir Kara-Murza -- jailed in April for denouncing the war -- has been charged with high treason, his lawyer told the TASS news agency.
The UN nuclear agency chief was due in Kyiv to discuss creating a security zone around Ukraine's Zaporizhzhia atomic plant -- the largest in Europe -- after Russian President Vladimir Putin ordered his government to impound it.