Russia has launched around 200 missiles and drones at Ukraine, killing five people and striking energy facilities across the country, reports Kyiv.
Power cuts and water supply outages were reported in many areas of Ukraine following the major strike on Monday, including parts of Kyiv.
Officials said the attack - which comes two-and-a-half years into Russia's full-scale invasion - targeted power or other critical infrastructure in at least 10 regions.
Russia dramatically stepped up its strikes on the Ukrainian power grid in March in what Kyiv has said looked like a concerted effort to degrade the system ahead of the winter, when people need electricity and heating most.
Monday's missile and drone attack was Russia's most intense in weeks, coming as Ukraine is claiming new ground in a major cross-border incursion into Russia's southern Kursk region. Meanwhile Russian forces have been steadily inching forward in eastern Ukraine, closing in on the transport hub of Pokrovsk.
President Volodymyr Zelensky said on Telegram: “It was one of the biggest combined strikes.
“More than a hundred missiles of various types and about a hundred Shahed drones. And like most previous Russian strikes, this one is just as sneaky, targeting critical civilian infrastructure.”
Mr Zelensky said the energy sector had suffered "a lot of damage".
Poland said an "object" had also entered its airspace, that it may have landed on Polish territory and that searches were underway.
"Most likely it was a drone and we assume so, because the trajectory of the flight and the speed indicate that it was definitely not a missile," Jacek Goryszewski, spokesperson for the Polish army's operational command, told news agency Reuters.
According to Prime Minister Denys Shmyhal, 15 Ukrainian regions sustained damage from the missile and drone barrage.
Top Kyiv officials urged its Western allies and arms suppliers to allow long-range strikes into Russia. Mr Zelensky also redoubled his call on allies such as Poland to join Ukraine in shooting down missiles and drones over Ukrainian airspace.
Both Russia and Ukraine deny deliberately targeting civilians. Each says its attacks are aimed at destroying infrastructure critical to the other's war effort.
Russia's defence ministry said on Monday its forces used high precision weapons to strike important energy infrastructure in Ukraine which it said supported the military-industrial complex. It listed power substations, gas compressor stations and storage sites for aircraft weapons.
The regions reporting strikes on power or critical infrastructure included Rivne and Volyn in the northwest, Khmelnytsk in the southwest, Zhytomyr in the north, Lviv in the west, Dnipropetrovsk, Kirovohrad and Vinnytsia in central Ukraine, Zaporizhzhia in the southeast and Odesa in the south.
Neighbouring Moldova, whose grid is linked to that of Ukraine, reported small disruptions to its power network.
Ukraine's foreign ministry said a hydropower plant in the Kyiv region had been targeted too.
A video posted on social media and verified by Reuters showed a damaged dam and a fire after an apparent strike at a hydropower plant. A separate clip, also verified, showed a missile hitting a water reservoir.
The Kyiv region governor Ruslan Kravchenko said in televised comments there was no critical damage to the dam.
In the northeastern Sumy region - from where Ukraine launched its major incursion into Russia on August 6 - authorities said a railway infrastructure facility had been struck, but did not give further details.
A 69-year-old man in the Dnipropetrovsk region and a man in the Zaporizhzhia region were among at least five people confirmed dead, local officials said. The others were in the regions of Kharkiv, Zhytomyr and Volyn.
In Lutsk, an apartment block was damaged, the mayor said after reporting explosions.
Blasts also shook central Kyiv and air defences could be heard engaging incoming targets on the outskirts of the capital.
The air force said Russia used 11 TU-95 strategic bombers during Monday's attack, as well as other weaponry.
Approximately 15 missiles and almost 20 drones targeting the capital of Kyiv were shot down, according to Serhiy Popko, head of Kyiv's military administration.
