Russia on Saturday bombed a hardware superstore in the eastern Ukrainian city of Kharkiv, killing two people and wounding more than 30, Ukraine officials said, in an attack condemned as "vile" by President Volodymyr Zelensky.
Kharkiv regional governor Oleg Synegubov said at least two people were killed when two guided Russian bombs hit the store.
"Two people were killed. They were men who worked in the hypermarket," Synegubov said in a video posted on Telegram.
"The number of wounded has gone up to 35 people," Kharkiv's mayor, Igor Terekhov, posted on Telegram.
Thick black smoke billowed from the gutted building of the Epitsentr DIY superstore in the northeastern outskirts of the city, as firefighters sprayed water on a blaze sparked by the strikes, an AFP journalist saw.
The Epitsentr chain sells household and DIY goods.
"As of now, we know that more than 200 people could have been inside the hypermarket," Zelensky said on Telegram, condemning the daylight attack on an "obviously civilian" target.
The regional governor said there was "no contact with some of the staff" and "according to our information, visitors could still be in the building".
Kharkiv, Ukraine's second-largest city, is just a few dozen kilometres from the border and regularly comes under attack from Russian missiles -- strikes on the city killed seven people Thursday.
Later Saturday, another strike hit the centre of Kharkiv, injuring eight, Terekhov said, without giving details.
Zelensky had visited Kharkiv on Friday and met officials to discuss the defence of the surrounding region.
On Saturday, he urged world leaders to supply Ukraine with "sufficient air defence protection" to "prevent such terrorist attacks".
"Russia struck another brutal blow at our Kharkiv -- at a construction hypermarket -- on Saturday, right in the middle of the day," Zelensky said.
"Only madmen like Putin are capable of killing and terrorising people in such a vile way," he added, referring to the Russian president who ordered his troops into Ukraine in February 2022.
The latest attacks came after Russia launched a ground offensive in the Kharkiv region on May 10. Ukraine said Friday that it had managed to halt Moscow's progress and was counterattacking.
Ukraine's rescue service posted images of firefighters spraying water inside the blazing Epitsentr store building, with the roof torn open and debris strewn around.
They said the fire had raged over an area of 10,000 square metres (108,000 square feet) but that the firefighters had managed to contain it.
"There were a lot of workers and shoppers inside," Zelensky said.
Terekhov, Kharkiv's mayor, said that according to the store's owner, 15 employees had not been in contact and approximately 200 people were in the building at the time of the strikes.
He described the attack as "pure terrorism".
Russia and Ukraine accused each others' forces of attacks in the border area Saturday.
Russia said that Ukraine shelled a small town in the Belgorod border region, killing two and wounding 10.
Ukraine said Russia shelled the village of Kupiansk-Vuzlovyi, a railway hub in the Kharkiv region near the border, wounding five, the regional prosecutor's office said.
It said two vehicles came under fire: a car with two passengers and an ambulance with a driver, a paramedic and a 64-year-old patient.
Russia also carried out air strikes on the Kupiansk district, damaging a factory and residential buildings, prosecutors said.
In the eastern Donetsk region, shelling on Saturday killed a 40-year-old woman and wounded four, said the head of the regional administration, Vadym Filashkin.
