KYIV, Ukraine — Ukraine sent waves of drones deep into western Russia in more than four hours of nighttime attacks that struck military assets, Russian officials and media reports said Wednesday.

The drones hit an airport near Russia’s border with Estonia and Latvia, causing a huge blaze and damaging four Il-76 military transport planes, the Russian state news agency Tass reported, citing emergency officials.

With at least six regions targeted, the barrage appeared to be the most extensive Ukrainian drone attack on Russian soil since the war began 18 months ago, although no injuries were reported. The Kremlin has repeatedly accused Ukraine of cross-border incursions on the Belgorod region of Russia and of launching drones toward Moscow.

There was no immediate comment from Ukrainian officials, who usually don’t claim attacks inside Russia. The Kremlin’s forces, meanwhile, hit Kyiv with drones and missiles during the night in what Ukrainian officials called a “massive, combined attack” that killed two people.

Aerial attacks on Russia have escalated recently as Ukraine pursues a counteroffensive. Kyiv increasingly targets Russia’s military assets behind the front lines in eastern and southern Ukraine.

Ukraine has also claimed to have used naval drones against Russian ships in the Black Sea. Ukrainian media said Kyiv saboteurs used drones last week to hit bomber aircraft parked at air bases deep inside Russia.

The airport in the Pskov region, about 400 miles north of the Ukrainian border and 400 miles west of Moscow, suffered the most damage in the overnight attacks.

Smoke from a massive fire billowed over the city of Pskov, the region’s namesake capital, according to social media posts, including video of loud bangs and flashes, along with the crackle of air defense systems and tracers in the night sky.

Pskov Gov. Mikhail Vedernikov ordered all flights to and from the airport canceled for the day to assess damage, which he later said was not major, adding that normal operations would resume Thursday.

Other regions hit were Oryol, 240 miles south of Moscow, as well as Ryazan and Kaluga, which are both 20 miles south of the capital. Also hit was Bryansk, which borders Ukraine, according to the Russia Defense Ministry.

Three main Moscow airports — Sheremetyevo, Vnukovo and Domodedovo — temporarily halted incoming and outgoing flights.

The Associated Press was unable to confirm whether the drones were launched from Ukraine or inside Russia.

Mykhailo Fedorov, Ukraine’s minister of digital transformation, said his country has drones with a range of up to 300 miles, although he did not take responsibility for any attacks in Russia or Crimea, the peninsula that Russia illegally annexed from Ukraine in 2014.

“If you look carefully at the news recently, in general, every day there are news about long-range drones that hit various targets both in occupied Crimea and in the territory of Russia,” Fedorov told AP recently. “So in this regard, let’s say, that more or less a mass production of these drones has appeared.”

Kremlin spokesman Dmitry Peskov said the Russian military would undoubtedly analyze “how this was done in order to take appropriate measures to prevent these situations in the future.”

Firing at distant Russian targets could reflect a Ukrainian tactic of stretching the Kremlin’s military resources as Moscow scrambles to buttress its air defenses, said Douglas Barrie, senior fellow for military aerospace at the International Institute for Strategic Studies.

“Putting air defense systems there means you can’t put them somewhere else,” he told AP. “This draws on Russian capability.”

Russia’s Foreign Ministry spokeswoman Maria Zakharova said Ukraine was relying on foreign help because the drones “simply would not be able to fly such a distance without carefully researched information from Western satellites.”