KYIV and LONDON — The Security Service of Ukraine (SBU) conducted a large-scale operation targeting four Russian military airfields on Sunday, an SBU source confirmed to ABC News, claiming to have hit more than 40 military aircraft “that bomb Ukrainian cities every night.”

The governors of the Russian regions of Irkutsk and Murmansk confirmed drone attacks in their respective regions. Videos shared with ABC News by the SBU showed drones attacking Olenya airbase in Murmansk and Belaya airfield in Irkutsk. Both are home to Russian strategic bomber aircraft, including nuclear-capable bombers.

The governor of Irkutsk noted that the drones were launched from the back of a truck in the area. The governor posted an accompanying video of drones flying overhead and huge columns of smoke rising nearby.

A source in the SBU told ABC News that the operation had been planned for “more than a year and a half.” Drones were concealed inside makeshift “mobile houses” with retractable roofs, which were then placed on trucks.

“At the right moment, the roofs of the houses were remotely opened and the drones flew out to strike,” the source said.

In a statement posted to the social media site Telegram, the Russian Ministry of Defense acknowledged what they called a “terrorist attack using FPV drones against airfields in the Murmansk, Irkutsk, Ivanovo, Ryazan and Amur regions.”

“[S]everal units of aircraft caught fire” in the Murmansk and Irkutsk regions “as a result of the launch of FPV drones from the territory located in the immediate vicinity of the airfields,” according to the statement.

The statement, which attributed the attacks to the “Kyiv regime,” said that “attacks were repelled” at “military airfields in the Ivanovo, Ryazan and Amur regions.”

“The fires have been extinguished. There are no casualties among military personnel or civilian personnel,” the statement said, adding that “some of the participants in the terrorist attacks have been detained.”

Ukrainian President Volodymyr Zelenskyy posted a statement to the social media site X about Sunday’s drone attack, saying in part that it produced “an absolutely brilliant result.” He added that Ukrainian military officials involved in preparing the operation were “withdrawn from Russian territory in time” and that the drone strikes “will undoubtedly be in the history books.”

The drone strikes come as Russia-Ukraine peace talks are scheduled to resume on Monday in Istanbul, Turkey.

“Ukraine is defending itself, and rightly so — we are doing everything to make Russia feel the need to end this war,” Zelenskyy said, adding, “Russia started this war, Russia must end it.”

Elsewhere, at least seven people were killed and 66 injured when a railway bridge collapsed and a train derailed in Russia’s western Bryansk region overnight, following what one local official said was “an explosion” on the route.

Train operator Moscow Railway said the number 68 passenger train was traveling from the Belgorod border town of Klimov to Moscow when it derailed “due to the collapse of the superstructure of the road bridge as a result of illegal interference in transport operations.”

“There was an explosion on the bridge on the highway while the Klimov-Moscow train was moving, which had 388 passengers on board,” Bryansk Gov. Aleksandr Bogomaz said during an interview on the Rossiya-24 TV channel, as quoted by the state-run TASS news agency.

Bogomaz said on Telegram that seven people were killed and 66 people were injured, 47 of whom were hospitalized

A second railway bridge collapsed overnight in the Russian region of Kursk — another border region neighboring Bryansk to its north — derailing a passing freight train.

“Part of the train fell onto a road underneath the bridge,” Alexander Khinshtein, the acting regional governor, said. At least one worker was injured, he added.

Andrei Klishas, the chairman of Russia’s Federation Council Committee on State Construction, claimed on Telegram that Ukraine was responsible for the deadly incident in Bryansk.

“The blowing up of the bridge and the derailment of the passenger train in the Bryansk region indicate that Ukraine is controlled by a terrorist group,” he wrote.

The Kremlin said in a statement that President Vladimir Putin “was briefed on the situation,” receiving updates from the Federal Security Service and the Emergencies Ministry.

Andriy Kovalenko, the head of the Counter-Disinformation Center operating as part of Ukraine’s National Security and Defense Council, disputed suggestions of Ukrainian involvement in a Telegram post — linking the allegations to Monday’s planned peace talks in Istanbul, Turkey.

“It seems that the Kremlin is preparing the ground for the disruption of the talks,” Kovalenko wrote. “Ukraine has no motive to disrupt the Istanbul summit. On the contrary, Ukraine agreed to a ceasefire long ago. Therefore, a rail war in the style of World War II is an argument for Russian propaganda, not an instrument of our policy.”

Ukrainian intelligence services have in the past claimed responsibility for attacks on Russia’s railway networks intended to hamper Moscow’s military logistics, while also sharing reports of arson and other sabotage operations against Russian railways without explicitly claiming responsibility.

On Sunday, for example, Ukrainian military intelligence — GUR — reported an explosion on a railway in occupied southern Ukraine on Saturday night, which it said derailed a freight train that was heading toward occupied Crimea.

“As a result of an explosion on the railway track, the train with fuel tanks and freight cars derailed,” the GUR said in a statement. “The key logistical artery of Muscovites in the occupied territories of Zaporizhzhia region and Crimea was disrupted.”

“The fight against the military logistics of the Russian occupiers continues,” the GUR statement added.

Ukrainian strikes in the Russian border regions of Bryansk, Kursk and Belgorod have become commonplace over more than three years of Moscow’s full-scale invasion of its neighbor. These have included ground incursions by Ukrainian forces, most notably in the Kursk region.

Meanwhile, Moscow also continued its own long-range strike campaign against Ukraine. The Ukrainian air force reported 479 drones and missiles launched into the country overnight, marking one of — if not the — largest overnight aerial attack of the 3-year-old war.

The air force said it neutralized 385 of the “aerial attack assets,” but added that “impacts” were recorded in 18 places.

The Ukrainian Ground Forces also reported a Russian missile strike on a military training facility in an undisclosed location in Ukraine, in which 12 people were killed and 60 injured.

ABC News’ Victoria Beaule, Natalia Popova and Oleksiy Pshemyskyi contributed to this report.