• As Russia prepares to celebrate Victory Day, its airports were plunged into chaos by drone attacks.
• At least 350 flights were canceled or delayed for hours, a Russian tourism body said.
• Russia's Defense Ministry said it shot down hundreds of Ukrainian drones on Wednesday.

At least 60,000 passengers had their flights delayed or canceled at airports across Russia as Ukraine unleashed large-scale drone attacks this week, according to a national tourism body.

Russia's association of tour operators said in a statement on Wednesday that at least 350 flights were affected by the threat of drone strikes, including trips out of the country to destinations such as Istanbul and Dubai.

The affected facilities included Moscow's four airports and air travel hubs in the regions of Sochi, Kazan, and Kirov, per the association. Its statement said many of the flights were delayed overnight, while some flights that did manage to depart had to wait up to seven hours.

Russian independent Telegram news channels posted photos of large crowds gathering in airports and stranded passengers resting in departure hall areas.

"This delay will provoke subsequent delays according to the domino principle," the tourism operators' association warned.

"The aviation infrastructure is working at its limit," it added.

It advised travelers across the country to prepare for further disruption by bringing cash to buy food and drink at airports and taking a "small supply" of water with them.

The chaos comes as Russia is set to hold an annual Victory Day parade on May 9 that commemorates the Soviet Union's role in ending World War II — a major source of national pride promoted by Moscow nowadays.

Russia says it's expecting 29 world leaders to attend the parade, including Chinese leader Xi Jinping, who arrived on Wednesday afternoon.

Meanwhile, Kyiv has warned visiting leaders that it can't guarantee their safety if they fly into Moscow, which has been harassed by Ukrainian drone strikes for years.

"We cannot be held responsible for what happens on the territory of the Russian Federation," Ukrainian President Volodymyr Zelenskyy told reports on Saturday.

The week leading up to Russia's Victory Day parade has seen Ukraine launch an intensified series of drone strikes over three consecutive days.

They appear to be ramping up in severity, with the Kremlin saying on Wednesday that it shot down 524 drones. Business Insider couldn't independently verify that figure, but if accurate, it would record one of Ukraine's largest drone attacks on Russian territory.

Oleksandr Kovalenko, a popular Ukrainian military observer, wrote on his Telegram channel that Wednesday involved the "most massive raid of Ukrainian attack drones" since the full-scale war began. However, he also accused Russian reports of overplaying the number of drones launched by Ukraine.

Moscow's mayor, Sergei Sobyanin, wrote in his Telegram channel that Russian forces had repelled at least 14 drone attacks on the capital on Wednesday. Emergency services were dispatched to several locations where debris had fallen, he added.

No casualties were reported as of press time.

Previous Ukrainian drone attacks have caused Moscow's airports to close before, including a wave of strikes in September that shut three of the region's four air travel hubs.

Russia also regularly attacks Ukrainian cities, primarily with ballistic missiles and Iranian-designed Shahed exploding drones. Most recently, Kyiv reported that a mother and son were killed during a missile and drone attack on Tuesday evening.

• Ukraine said it hit Russia's Engels-2 air base, causing fires and explosions.
• Engels-2 is a key Russian base used for launching bomber attacks on Ukraine.
• While Ukraine attacked the military base, Russia bombed a Ukrainian city overnight.

Ukraine claimed responsibility for a major attack that set a blaze at a key Russian air base overnight on Wednesday.

The General Staff of the Armed Forces of Ukraine said Thursday that its special forces had caused the detonation of an ammunition store at the Engels-2 air base in Russia's Saratova region, resulting in fires and explosions.

Engels-2, which sits about 450 miles from unoccupied Ukraine, is a key air base from which Russia has launched devastating attacks on Ukraine using its fleet of Tu-95 and Tu-160 bomber aircraft.

It's unclear if any planes were damaged in the attack.

Ukraine's General Staff didn't say what weapons were used, but the region's governor, Roman Busargin, said that Russian forces had shot down 54 drones.

He called it the largest attack on the area since 2022. Russian authorities do not generally report on strikes.

Busargin said in a Telegram post Thursday that a state of emergency had been declared, and that civilians had been evacuated from areas around the base.

Russian opposition media channel Astra shared images and video of a massive plume of smoke and reported multiple explosions.

The blasts knocked windows out of two kindergartens, a school, and a local hospital, injuring one woman, Busargin said.

Business Insider could not independently verify the reports.

Ukraine's attack on the base came amid a wider barrage, with Russia's Ministry of Defence claiming to have shot down 134 drones overnight across six regions.

It was also the third attack on Engels-2 this year.

In January, Ukraine's 14th Unmanned Aerial Vehicle Regiment claimed responsibility for what it described at the time as its largest-ever attack on a Russian military facility, targeting an oil storage facility supplying fuel for the planes.

The base has taken extensive measures to try to protect the aircraft, including piling tires onto them in an apparent attempt to fool Ukrainian missiles.

In 2023, Russia relocated some of its bombers farther east, to avoid Ukrainian attacks.

Ukraine's General Staff said Thursday that it used detailed planning to avoid civilian casualties.

Russia also sent more than 200 attack drones and other missiles against central Ukraine overnight Wednesday, Ukrainian President Volodymyr Zelenskyy said on Telegram.

More than 30 explosions were heard in Kropyvnytskyi, a city in Kirovohrad Oblast, the regional governor told broadcaster Suspilne.

Police said that 10 people were injured in the attacks.