KYIV, Ukraine (AP) — The Ukrainian Security Service announced on Sunday that a drone attack orchestrated by Ukraine has annihilated over 40 Russian aircraft within Russian territory. Meanwhile, Russia retaliated with missile and drone strikes on Ukraine just before the commencement of new peace negotiations in Istanbul.

An anonymous military official who disclosed specifics to the Associated Press stated that the intricate operation, under direct supervision by Ukrainian President Volodymyr Zelenskyy, took more than 18 months to come to fruition.

The operation was described by the source as “exceptionally challenging,” involving the covert transportation of first-person view (FPV) drones into Russia, where they were concealed inside mobile wooden structures.

“Later, drones were hidden under the roofs of these houses while already placed on trucks. At the right moment, the roofs of the houses were remotely opened, and the drones flew to hit Russian bombers,” the source said.

Social media footage shared by Russian media appeared to show the drones rising from inside containers while other panels lay discarded on the road. One clip appeared to show men climbing onto a truck in an attempt to halt the drones.

The drones hit 41 planes stationed at military airfields on Sunday afternoon, including A-50, Tu-95 and Tu-22M aircraft, the official said. Moscow has previously used Tupolev Tu-95 and Tu-22 long-range bombers to launch missiles at Ukraine, while A-50s are used to coordinate targets and detect air defenses and guided missiles.

The Security Service of Ukraine said that the operation, which it codenamed “Web”, had destroyed 34% of Russia’s fleet of air missile carriers with damages estimated at $7 billion. The claim could not be independently verified.

Russia’s Defense Ministry in a statement confirmed the attacks, which damaged aircraft and sparked fires on air bases in the Irkutsk region, more than 4,000 kilometers (2,500 miles) from Ukraine, as well as the Murmansk region in the north, it said. Strikes were also repelled in the Amur region in Russia’s Far East and in the western regions of Ivanovo and Ryazan, the ministry said.

The attack came the same day as Zelenskyy said Ukraine will send a delegation to Istanbul for a new round of direct peace talks with Russia on Monday.

In a statement on Telegram, Zelenskyy said that Defense Minister Rustem Umerov will lead the Ukrainian delegation. “We are doing everything to protect our independence, our state and our people,” Zelenskyy said.

Ukrainian officials had previously called on the Kremlin to provide a promised memorandum setting out its position on ending the war before the meeting takes place. Moscow had said it would share its memorandum during the talks.

Also on Sunday, Russia’s top investigative body said that explosions had caused two bridges to collapse and derailed two trains in western Russia overnight, killing seven in one of the incidents and injuring dozens more. Russian officials, however, did not say what had caused the blasts and the word “explosions” was later removed from an Investigative Committee press release.

Russian strike hits an army unit

Russia on Sunday launched the biggest number of drones — 472 — on Ukraine since the full-scale invasion in February 2022, Ukraine’s air force said.

Russian forces also launched seven missiles alongside the barrage of drones, said Yuriy Ignat, head of communications for the air force. Earlier Sunday, Ukraine’s army said at least 12 Ukrainian service members were killed and more than 60 were injured in a Russian missile strike on an army training unit.

The strike occurred at 12:50 p.m., the statement said, emphasizing that no formations or mass gatherings of personnel were being held at the time.

Ukrainian army commander Mykhailo Drapatyi later Sunday submitted his resignation following the attack. He was a respected commander whose leadership saw Ukraine regain land on the eastern front for the first time since Kyiv’s 2022 counteroffensive.

The training unit was located to the rear of the 1,000-kilometer (620-mile) active front line, where Russian reconnaissance and strike drones are able to strike. Ukraine’s forces lack troops and take extra precautions to avoid mass gatherings as the skies across the front line are saturated with Russian drones looking for targets.

Northern pressure

Russia’s Ministry of Defense said Sunday that it had taken control of the village of Oleksiivka in Ukraine’s northern Sumy region. Ukrainian authorities in Sumy ordered mandatory evacuations in 11 more settlements Saturday as Russian forces make steady gains in the area.

Speaking Saturday, Ukraine’s top army chief, Oleksandr Syrskyi, said that Russian forces were focusing their main offensive efforts on Pokrovsk, Toretsk and Lyman in the Donetsk region, as well as the Sumy border area.