The city of Lutsk, which lies in Ukraine's northwest along the border with Poland and Belarus, was the hardest hit overnight, though 10 other regions were also struck, Ukrainian President Volodymyr Zelenskiy said on Wednesday.
Lutsk is home to airfields used by the Ukrainian army.
Cargo planes and fighter jets routinely fly over the city.
No casualties were immediately reported, as emergency crews continued to assess the damage.
Western regions of Ukraine are a crucial logistical backbone in the war, as airfields and depots there receive vital foreign military aid before forwarding it to other parts of the country.
Russian long-range attacks have increasingly sought to disrupt those supply corridors.
Russia has recently sought to overwhelm Ukrainian air defences by launching massive aerial assaults, including adding more decoy drones to its attacks.
Russia launched its previous largest aerial assault late in the night of July 4 into the following day, with the biggest prior to that occurring less than a week earlier.
Russia's bigger army has also launched a new drive to punch through parts of the 1000km front line, where short-handed Ukrainian forces are under heavy strain.
US President Donald Trump said on Tuesday that he was "not happy" with Russian President Vladimir Putin, who has not budged from his ceasefire and peace demands since Trump took office in January and began to push for a settlement.
Trump said on Monday that the US would have to send more weapons to Ukraine, just days after Washington paused critical weapons deliveries to Kyiv amid uncertainty over the US administration's commitment to Ukraine's defence.
Zelenskiy said the Kremlin was "making a point" with the attack, as US-led peace efforts flounder.
He urged Ukraine's partners to impose stricter sanctions on Russian oil and those who help finance the Kremlin's war by buying it.
"Everyone who wants peace must act," Zelenskiy said.
Poland scrambled its fighter jets and put its armed forces on the highest level of alert in response to Russia's attack, the Polish Armed Forces Operational Command wrote in an X post.
Danish Prime Minister Mette Frederiksen warned on Tuesday that Russia could pose a credible security threat to the European Union by the end of the decade.
She called for defence industries in Europe and Ukraine to be ramped up within five years.
Ukraine's air defences shot down 296 drones and seven missiles overnight, while 415 more drones were lost from radars or jammed, an air force statement said.
Ukrainian interceptor drones, developed to counter Russia's Shahed drones, are increasingly effective, Zelenskiy said, noting that most targets were intercepted and that domestic production of anti-aircraft drones is being scaled up.
Western military analysts say Russia is boosting its drone manufacturing and could soon be capable of launching 1000 drones a night at Ukraine.
