KYIV, Ukraine — Ukraine sent waves of drones deep into western Russia in nighttime attacks that lasted more than four hours and 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, which can carry heavy machinery and troops, the Russian state news agency Tass reported, citing emergency officials.

With at least six regions of Russia 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 the Ukrainian military 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 take responsibility for 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 to drive out Moscow’s forces. 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 that Kyiv saboteurs used drones last week to hit bomber aircraft parked at air bases deep inside Russia.

City is 400 Miles from Moscow

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 so damage could be assessed. No one was hurt and the fire was put out, he said.

Other regions hit were Oryol, 240 miles south of Moscow, as well as Ryazan and Kaluga, which are both 120 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, though he did not take responsibility for any attacks inside Russia or on Crimea, which 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.”

Russia, meanwhile, also used drones as well as missiles in its biggest bombardment of Kyiv in months, Ukrainian authorities said.

Two security guards, ages 26 and 36, were killed and another person was injured by falling debris, said Serhiy Popko, head of Kyiv’s military administration, posting on Telegram.

Russia launched Iranian-made Shahed exploding drones at the capital from various directions and then followed with air-launched missiles, Popko said. It was unclear how many were fired, but Popko called it the biggest attack on the capital since spring.

Kyiv resident Iryna Oblat pointed to debris in the street and shattered windows in surrounding buildings.

“Look where it hit, look what happened to the house,” she said. “Garages are on fire. We don’t know how many cars and garages were destroyed because firefighters and police won’t let us in.”

Also on Wednesday, Russia-installed officials in Crimea reported repelling an attack of drones targeting Sevastopol’s harbor. Past drone attacks have hit fuel depots and airfields in Crimea or Russian-held areas of Ukraine.

Explosions also were reported in the southern city of Odesa and the Cherkasy region.

Ukraine’s air defenses destroyed 28 cruise missiles and 15 of 16 Shahed drones targeting Kyiv and multiple regions across the country overnight, the air force said in its daily Telegram update.