Russia reported its military had inflicted further heavy losses on Ukrainian troops and was closing in on the city of Lysychansk on Wednesday.
The day's fighting was largely concentrated on eastern Ukraine's Donbass region, though Russian missiles also rained down with unusual intensity on other parts of the country.
There were multiple strikes against civilian infrastructure reported, though it remained impossible to independently verify most battlefield reports.
Russia reported it had killed all but 30 members of a 350-strong Ukrainian brigade during a fight for control of an oil refinery in the Luhansk region city of Lysychansk on Wednesday.
Russian forces also reported destroying a "training centre for foreign mercenaries" near the southern Ukrainian city of Mykolaiv, along with four command posts.
At least three people were killed and another five injured in a Russian missile attack on the city, the region's military governor reported earlier.
Russia also claimed it had killed 100 Ukrainian soldiers and destroyed military equipment in fighting near the town of Pitomnik, in Ukraine's Kharkiv region.
Despite these claims, there were no reports of Russian territorial gains.
After six Russian missiles were fired at the city of Dnipro on Tuesday, rescuers discovered the bodies of a man and a woman under the rubble of an impacted building, the governor of the Dnipropetrovsk region, Valentyn Reznichenko, wrote on Telegram.
Ukraine is still reeling from a Russian airstrike on a shopping centre in the city of Kremenchuk earlier this week that left at least 20 civilians dead and attracted furious international condemnation.
While Russia did not deny its missile struck the facility, it said it had been aiming for a military site nearby and disputed the claim that the mall was in operation at the time.
British Ministry of Defence officials said it was possible Russian forces had not intended to strike a civilian target in the attack, noting that Russian missiles were not known for their precision.
However, in a series of tweets on Wednesday, they also added that Russia appeared to accept the necessity of collateral damage in its bid to occupy Ukraine.
Elsewhere, the pro-Russian military administration of Ukraine's Kherson region said that it was preparing to hold a referendum on becoming a "fully-fledged member" of Russia.
Ukraine's government has long expected that such a referendum could be on the cards for Kherson, which has been under Russian control since early March. Similar votes were previously held to legitimize Russian occupation of the annexed Crimean Peninsula and the eastern Ukrainian separatist regions of Luhansk and Donetsk.
According to reports that emerged on Tuesday, the mayor of Kherson, Igor Kolykhaiev, was detained by Russian forces in what his assistant Galina Liashchevska described as an "abduction."
Despite the ongoing fighting, Ukrainian and Russian militaries exchanged a total of almost 300 prisoners of war on Wednesday, according to statements by both sides confirming the return of 144 captured soldiers.
According to the Ministry of Defence in Kiev, the released Ukrainian soldiers included 95 fighters involved in the siege of the Azovstal steelworks in Mariupol.
While internationally much of the diplomatic focus was on the NATO summit in Madrid on Wednesday, Russian ally Syria made a surprise announcement that it had officially recognized the pro-Russian separatist regions of Luhansk and Donetsk in eastern Ukraine as independent countries, becoming only the second country to have done so.
"The Syrian Arab Republic decided to recognize the independence and sovereignty of the Luhansk People's Republic and the Donetsk People's Republic," Syrian state news agency SANA reported, citing an official source at the Foreign Ministry in Damascus.
Shortly before invading Ukraine at the end of February, Russian President Vladimir Putin recognized both separatist regions as independent countries and later claimed to be protecting their sovereignty.
