Russia claimed on Sunday to have captured the strategic Ukrainian city of Lysychansk and the entire frontline Luhansk region as a mayor said six people were killed by Russian shelling to the west.
The gains claimed by Russia would mark a decisive breakthrough for Moscow's forces seeking control of eastern Ukraine, more than four months into their invasion and after turning their focus away from the capital Kyiv.
The mayor of Sloviansk, 75 kilometres (45 miles) west of Lysychansk, reported the heaviest Russian shelling "for a long time," saying that a child was among six people killed, with another 15 people wounded and 15 fires sparked.
On Sunday, Russia accused Ukraine of firing three cluster missiles at the city of Belgorod, near the Ukrainian border and late Saturday, Belarus said it intercepted Ukrainian missiles.
Lysychansk had been the last major city in the Luhansk area of the Donbas still in Ukrainian hands and its capture would signal a deeper push into the eastern region.
"Sergei Shoigu has informed the commander in chief of the Russian armed forces, Vladimir Putin, of the liberation of the People's Republic of Lugansk," the Russian defence ministry said in a statement quoted by Russian news agencies.
A few minutes prior to the announcement, which AFP has not verified, a spokesman for the Russian defence ministry had said fighting was ongoing in Lysychansk and that Ukrainian forces were "completely" surrounded.
Ukraine has yet to comment on the Russian claim that Lysychansk has fallen.
On Saturday, there were conflicting reports about Lysychansk's status with Ukraine denying Moscow's claim to have encircled the entire city, which lies just across the river from neighbouring Severodonetsk which Russian forces seized last week.
The city of Siversk, 30 kilometres west of Lysychansk, saw overnight shelling, residents and an official told AFP.
"It was intense and it was shooting from all sides," said a woman sheltering in a cellar.
"Fierce fighting continues along the entire frontline, in Donbas," Ukrainian President Volodymyr Zelensky said in an address late Saturday, accusing "enemy activity" of "intensifying" in the wider region around Ukraine's second city of Kharkiv.
Two people were killed and three wounded -- including two children -- in a strike on the town of Dobropillya, local authorities in Donetsk said.
On Monday, leaders from dozens of countries and international organisations set to gather in the Swiss city of Lugano for a conference on Ukraine's reconstruction with the aim of providing a roadmap for the war-ravaged country's recovery.
Zelensky said "colossal investments" would be needed and that 10 regions of Ukraine had been affected in the war, with many towns and villages needing to be "rebuilt from scratch".
Ukraine will also face demands for broad reforms, especially in cracking down on corruption after Brussels recently granted Kyiv candidate status in its push to join the 27-member bloc.
On Sunday, Moscow said its anti-aircraft defences shot down three Tochka-U cluster missiles launched by "Ukrainian nationalists" against Belgorod, close to the Ukrainian border.
Belgorod governor Vyacheslav Gladkov said 11 residential buildings and 39 houses were damaged.
Russia has previously accused Kyiv of conducting strikes on Russian soil, particularly in the Belgorod region. (AFP)