Ukraine has claimed responsibility for a drone attack in Russia's Tatarstan region - more than 1,300km (807 miles) from the Ukraine-Russia border.
The strikes, in which 12 people were injured, are the deepest into Russian territory since the start of the war.
Local authorities said that the strikes hit the town of Yelabuga, where drones are thought to be produced, and an oil refinery in nearby Nizhnekamsk.
The attacks occurred around 05:45 local time (02:45 GMT).
Yelabuga is located in the Alabuga "special economic zone" - an area with a special legal system aimed at attracting foreign investment. Iranian Shahed drones - which are frequently used by Russia to attack Ukraine - are thought to be assembled in Yelabuga.
According to media reports, at least 12 people - all of them students - were injured in Yelabuga.
Tatarstan regional leader Rustam Minnikhanov said the drones caused "no serious" damage to infrastructure in either location and that production operations were unaffected.
However, Ukraine's military intelligence said the strike in Yelabuga "caused significant destruction of production facilities".
Shortly after the attacks, a video circulated online purporting to show a light aircraft - thought to have been modified to fly unmanned - descending onto a building in Yelabuga before exploding, sending a fireball into the air.
On Tuesday morning, drones were also spotted in the Lipetsk region south of Moscow and an air raid alert was introduced, local authorities said.
For several months now, Kyiv has been ramping up its drone attacks on Russian territory.
Ukraine has warned repeatedly that its army is facing severe ammunition shortages, but has set a target of producing a million drones domestically this year.
Earlier this year, Ukraine was reportedly able to hit a major gas export terminal near the city of St Petersburg, 1,250km (775 miles) from the Ukraine-Russia border.
