Ukrainian President Volodymyr Zelenskiy said 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.
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.
Zelenskiy on Wednesday condemned the overnight attack and called for "biting" sanctions against Moscow and Russian oil.
"This is a telling attack - and it comes precisely at a time when so many efforts have been made to achieve peace, to establish a ceasefire, and yet only Russia continues to rebuff them all," he posted on X.
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.
US President Donald Trump said Tuesday that he's "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 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.
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, were increasingly effective, Zelenskiy said, noting that most targets were intercepted and that domestic production of anti-aircraft drones was being scaled up.
It is unusual for Russia to target western parts of Ukraine.
Western military aid to the country, including air defence systems, ammunition, and spare parts, is typically delivered overland through Poland and other neighbouring NATO countries.
These supplies are received at logistics hubs and airfields in western Ukraine.
From there, Ukrainian forces transport the equipment to the front lines or strategic sites across the country.
The relative safety of western regions has made them a crucial logistical backbone for sustaining Ukraine's defence, though recent long-range attacks by Russia have increasingly sought to disrupt these corridors.
