Blasts Sunday in a Russian city bordering Ukraine have killed at least three people, Russian officials said.
Dozens of residential buildings were damaged in the explosions in Belgorod. Russian lawmaker Andrei Klishas has called for a military response to the blasts.
'The death of civilians and the destruction of civilian infrastructure in Belgorod," Klishas posted on Telegram, "are a direct act of aggression on the part of Ukraine and require the most severe -- including a military -- response.'
Ukrainian officials have traditionally said very little about attacks on Russia.
Meanwhile, the mayor of the occupied Ukraine city of Melitopol, Ivan Fedorov, said on Telegram that Ukraine had hit one of four Russian military bases in the occupied territory.
Heavy fighting raged in Ukraine's eastern Donbas region Saturday as Russian forces increased their bombardment of the city of Lysychansk. Russia is targeting the area as its military looks to push deeper into the industrial region, which has become the focus of its latest offensive since failing to capture Kyiv after its Feb. 24 invasion.
Ukrainian separatists backed by Russia said they had encircled the city.
'Today the Lugansk popular militia and Russian forces occupied the last strategic heights, which allows us to confirm that Lysychansk is completely encircled,' Andrei Marotchko, a representative for the separatist forces, told Tass.
Hours after that statement, the Ukrainian army denied Lysychansk had been surrounded, but said heavy fighting was ongoing on the outskirts of the city.
'Now there are fierce battles near Lysychansk, however, fortunately, the city is not surrounded and is under the control of the Ukrainian army,' Ukraine National Guard representative Ruslan Muzychuk told Ukrainian national television, according to Reuters.
'Definitely they are trying to demoralize us," a Ukrainian soldier returning from Lysychansk told Reuters. "Maybe some people are affected by that, but for us it only brings more hatred and determination.'
Russian forces seized Lysychansk's sister city, Sievierodonetsk, last month, after some of the heaviest fighting of the war.
In his nightly television address on Saturday, Ukrainian President Volodymyr Zelenskyy urged Ukrainians to maintain their resolve and inflict losses on the 'aggressor ... so that every Russian remembers that Ukraine cannot be broken.'
'In many areas from the front, there is a sense of easing up, but the war is not over,' he said. 'Unfortunately, it is intensifying in different places, and we mustn't forget that. We must help the army, the volunteers, help those who are left on their own at this time.'
Along with the Lysychansk and Bakhmut areas, the Kharkiv region is seeing some of the front line's worst fighting. Four people were killed, and three others were wounded in shelling in Izium and Chuguiv, two districts of the northeastern Kharkiv region, according to Oleg Synegubov, Kharkiv chief of district. Russian rockets also struck residential properties in Sloviansk, killing a woman in her garden and wounding her husband, according to a neighbor who spoke with Agence France-Presse.
In Kharkiv, missiles hit some railway infrastructure, but no casualties were reported. The strike damaged railroad tracks and knocked down high voltage power lines.
"After Russian rockets hit at 4 in the morning, the power grid and three high-voltage lines powering traffic lights and [a] substation are damaged," Pavlo Svistelnikov, manager of the regional power grid, told Reuters. Russian forces have been pounding the city for over a week, killing civilians and hitting apartment buildings and schools, regional authorities said.
The mayor of the southern region of Mykolaiv, which borders the vital Black Sea port of Odesa, reported powerful explosions in the city.
Russia later said it had hit army command posts in the area, but Reuters could not independently verify that report.
After a missile struck an apartment building in Odesa on Friday, Zelenskyy accused Russia of state terror.
"I emphasize, this is an act of deliberate, purposeful Russian terror and not some kind of mistake or an accidental missile strike," Zelenskyy said. The death toll in that Odesa strike has risen to 21.
Ukrainian military officials said at least 50 civilians have been killed by Russian rocket and missile attacks this week, including 19 killed Monday in a mall in Kremenchuk.
Zelenskyy's comments came as Ukrainian authorities released video Saturday of Russian fighter jets bombing Snake Island a day after Russia said it had retreated from the island on humanitarian grounds.
Russia also launched new bus service from Crimea to newly seized cities in the eastern sections of Ukraine.
As the war continues the United States announced details of $820 million in additional military aid for Ukraine, including new surface-to-air missile systems and counter-artillery radar.
The 14th U.S. package of military aid includes two air defense systems, known as NASAMS, which can help Ukrainian forces defend against cruise missiles and aircraft.
The latest aid package is designed to help Ukraine counter Russia's use of long-range missiles and follows calls by Ukrainian officials for Western countries to send more advanced weapons systems that can better match Moscow's equipment.
A senior U.S. official said the systems are NATO-standard defense systems and are part of an effort to update Ukraine's air defenses from a Soviet-era system to a modern one.
Among other things, the latest military aid package provides Ukrainians with medium-range rocket systems the United States provided Ukraine in June.
Some information for this report came from The Associated Press, Reuters and Agence France-Presse.