A Russian strike on Kharkiv, Ukraine's second-largest city, killed six civilians and injured at least 10 others early on Saturday, regional officials said.
Ukraine's national police said the attack was launched by drones. It published pictures of blazes that had broken out on city streets and next to buildings.
"As of this morning, there are six dead and 10 wounded as a result of the night strike on Shevchenkivskyi district," Kharkiv Mayor Ihor Terekhov said on the Telegram messaging app.
"The attack hit residential areas — at least nine highrise buildings, three dormitories, a number of administrative buildings, a shop, a petrol station, a service station and cars were damaged," he said.
The strike occurred just after midnight, news reports said.
Ukraine's military said on Facebook its air defences destroyed 28 of 32 drones and three of six missiles launched by Russia.
The Russian military has not commented on the strikes, but said that Ukraine on Saturday morning fired Vampire rockets at Russia. All 10 of them were shot down over Russia's border region of Belgorod by air defence systems, the Russian Defence Ministry said.
Increased attacks
Kharkiv, in Ukraine's northeast, has been a frequent Russian target, with attacks intensifying in recent weeks. Earlier this week, a drone attack on the city killed four people and badly damaged apartment blocks.
Ukrainian President Volodymyr Zelenskyy's chief of staff, Andriy Yermak, told the news outlet Politico in an interview, published on Thursday, that he saw Kharkiv as the most likely target for any new Russian offensive in May or June.
Kharkiv regional governor Oleh Synehubov also reported a strike on a residential building and a missile attack on a village north of Kharkiv city. No casualties were reported in either incident.
Air raid alerts remained in effect for Kharkiv and most of the country, including the capital Kyiv, for several hours after the strikes.
Fierce battles continue elsewhere
On the ground in Ukraine, Russian forces were advancing, and pushing back against them was "difficult," said Oleksandr Syrskyi, commander of Ukraine's armed forces.
Syrskyi said the situation in the Bakhmut area in the partially occupied eastern Donetsk region was particularly challenging. He said Russian forces are carrying out offensive operations day and night, using assault groups with the support of armoured vehicles, as well as assaults on foot.
Fierce battles are taking place east of the town of Chasiv Yar, which Ukraine still controls and which is located near the occupied city of Bakhmut.
Russian forces are trying to break through defensive lines there, Syrskyi said on Telegram, adding that "Chasiv Yar remains under our control, all enemy attempts to break through to the settlement have failed."
Near Avdiivka, another city in the Donetsk region held by the Russians, the fiercest battles were occurring in Pervomaiskyi and Vodyanyi, according to the official. He also said the situation is tense on the southern and northeastern parts of the front line.
