Ukraine said it carried out its largest long-range attack with Russia on Sunday after launching a series of major strikes on four military bases using smuggled drones.
President Volodymyr Zelensky said the SBU security service used 117 drones in so-called "spider web" operations, shocking "34% of (Russia) strategic cruise missiles."
SBU sources earlier told BBC News that it took a year and a half to organize a strike involving drones hidden in wooden mobile cabins, roofs operated remotely on trucks, brought roofs near air conditioners and then fired at the right time.
Russia confirmed that Ukraine's attacks in five regions were called "acts of terror."
Meanwhile, Ukrainian authorities reported a one-night drone and missile attack on its territory.
All this is because negotiators from Russia and Ukraine will travel to Istanbul, Turkey for a second round of peace talks on Monday.
Expectations are low, as the two warring aspects are still far apart in how to end the war.
Russian President Vladimir Putin carried out a full-scale invasion of Ukraine in February 2022.
Moscow currently controls about 20% of Ukrainian territory, including the Crimean Peninsula annexed in 2014.
In several articles on social media late Sunday, Zelensky said he congratulated SBU chief Vasyl Maliuk for the "absolutely excellent result" of the surgery.
He said each of the 117 drones launched had their own pilot.
The Ukrainian president said: "The most interesting thing - we can already say publicly - our operations on Russian territory's 'office' are located next to the FSB in one of its regions."
FSB is Russia's powerful national security service.
Zelensky also said that all those involved in the operation were safely "strike" from Russia.
SBU estimates the damage to Russian Strategic Airlines is worth about $7 billion (£5 billion), and promises to release more details soon.
Ukraine's statement has not been independently verified.
Earlier on Sunday, SBU sources told the BBC in a statement that four Russian air bases, two of whom were thousands of miles from Ukraine, were attacked:
Among the popular Russian aircraft, it is a strategic nuclear bomber called the TU-95 and TU-22M3, as well as the A-50 early warning fighter, SBU sources said.
They describe the entire operation as “logically extremely complex.”
"The SBU first smuggled the FPV drone to Russia, followed by the mobile wooden pod. Once on Russian territory, the drones were hidden under the roofs of these cabins, which were already placed on vans," the source said.
"At the right moment, the roof was opened remotely and the drone took off and attacked the Russian bomber."
Irkutsk Governor Igor Kobzev confirmed that the drones that attacked the Belaya military base in Sredniy, Siberia were fired in trucks.
Kobzev posted on the telegram saying that the launch site has been protected and does not pose a threat to life.
Russian media also reported that other attacks emerged from trucks.
A user was heard saying that the drones were flying out of a Camas truck near the gas station.
Russian media reported on the attack in Murmansk but said air defense was working. The attack by Irkutsk was also reported.
In an article on social media late Sunday, the Russian Ministry of Defense confirmed that the air force tables in five regions of the country were attacks.
It claimed that “all attacks were encountered” at military air bases in the Ivanovo, Reshan and Amur regions. The latter basis is not mentioned by the SBU source.
The ministry said that after drones were launched from nearby areas, “several aircraft caught fire” in the Murmansk and Irkutsk regions.
It said all the fires were put out and no casualties were found. It added: “Some participants in the terrorist attack have been detained.”
Meanwhile, Ukrainian authorities said 472 drones and seven ballistic and cruise missiles were involved in a wave of attacks on Ukraine last night.
This appears to be one of the largest Russian drone attacks to date. Ukraine said it "neutralized" 385 aerial targets.
Ukraine's army said in another development that 12 of its military personnel were killed and more than 60 injured during a Russian missile strike at the training center.
Maj Gen Mykhailo Drapatyi, head of the Ukraine land force, will resign soon.
His decision, he said, was “a decision of my personal responsibility for the tragedy.”