Ukraine's military intelligence said Friday that a recent drone attack on an airport in northwestern Russia which damaged several transport planes was carried out from within Russian territory.
The claim came as Kyiv said police in the capital were responding to bomb threats as children returned to classrooms for a second academic year since Russia's invasion.
The attack this week on Pskov airport some 700 kilometres (more than 400 miles) from Ukraine marked the latest strike to rock Russian territory since Kyiv vowed to "return" the conflict to Russia in July.
"The drones used to attack the 'Kresty' air base in Pskov were launched from Russia," Ukraine's intelligence chief Kyrylo Budanov said on social media Friday.
"Four Russian IL-76 military transport planes were hit as a result of the attack. Two were destroyed and two were seriously damaged," he added.
Budanov said the aircraft had been used by the defence ministry to transport troops and cargo.
The Kremlin said this week that military experts were working to find out which routes drones are taking in order "to prevent such situations in the future".
Asked about Ukrainian claims on Friday, Kremlin spokesman Dmitry Peskov declined to comment and instead deferred questions to the defence ministry.
The region of Pskov, which was also targeted by drones in late May, is surrounded by NATO members Estonia and Latvia to its west and Belarus to its south.
- 'Calm' urged after bomb scare -
Budanov's comments came hours after Russian air defences destroyed a drone approaching Moscow, the city's mayor said, a day after a similar attack on the capital.
Russian media reported that air traffic at Moscow's Domodedovo and Vnukovo airports had been temporarily halted.
A recent uptick in aerial assaults have hit the capital's financial district, ripped holes in commercial buildings and even struck the Kremlin but officials have dismissed the increase in attacks.
The reports of bomb threats in Ukraine's capital came as the country's education ministry said nearly four million students were returning to school, both online and in person.
"We have received information about explosives in Kyiv's schools," police spokeswoman Yulia Girdvilis told AFP.
"All educational institutions are being checked by Kyiv police forces with the involvement of the State Emergency Service."
The police force said any evacuations would be decided by schools and the police, calling on people to "stay calm."
Ukrainian officials announcing the beginning of the new school year said that Russian attacks since the beginning of the invasion in February 2022 had damaged or destroyed thousands of schools.
Andriy Sadovy, the mayor of the western city of Lviv, said pupils will be learning to fly drones, releasing a picture of students behind computers.
"This is our new reality," he wrote on social media alongside images of children holding controllers and sitting in front of monitors simulating drone flights.
- Putin to host Erdogan -
Alongside the increase in drone attacks inside Russia, tensions have been building on the Black Sea after Moscow in July scrapped a deal allowing maritime exports from Ukraine.
But Ukraine has established an alternate route for cargo vessels and announced Friday that two more vessels had departed, defying a Russian naval blockade.
Turkey, which brokered the deal allowing grain exports from Ukraine with the United Nations, has urged Moscow to return to the accord.
The Kremlin announced Friday that Russian President Vladimir Putin will host his Turkish counterpart Recep Tayyip Erdogan in the Black Sea resort of Sochi for talks on Monday, likely on the scuppered agreement.
Turkey's Foreign Minister Hakan Fidan said on a visit to Moscow this week that reviving the deal to ship Ukrainian grain across the Black Sea was "critical" for global food security.