Several people were injured in an explosion at a residential building in the Russian city of St Petersburg on Saturday, as local media reported that a drone had been detonated.
Governor Alexander Beglow spoke only of an "incident" as he vowed to promised help to the residents of the flats that were damaged.
Six people had sought medical help and a 92-year-old woman was taken to hospital, the authorities said.
The explosion shattered some of the windows in the five-storey apartment building.
Residents of the flats were being housed in a kindergarten and treated by psychologists, according to reports.
Videos were shared on social media that showed a powerful explosion along with the audible sound of the blast, although the authenticity of the footage could not be verified.
The Russian Ministry of Defence did not comment on the incident.
The drone might have been aiming for a nearby oil storage facility, according to a report by St Petersburg news site Fontanka. The facility reportedly has a drone defence system.
In the evening, the governor of the Leningrad region bordering St Petersburg, Alexander Drosdenko, also reported on the deployment of air defence on the Gulf of Finland.
He published a video showing an explosion. The clip is supposed to show a drone being shot down by an anti-aircraft missile. There were no injuries or damage.
However, aircraft were briefly not allowed to land at Pulkovo Airport, it was reported.
As Ukraine tries to fend off the full-scale Russian invasion, it has attacked targets in the Russian hinterland several times, seeking to disrupt the supply of Russian troops.
Mostly, these attacks have been in Russian regions close to the border, although some targets have been hit deeper in the country.
Few drones have made it as far as St Petersburg, although Kiev has said that the range of Ukrainian drones is increasing.
The scale of damage wrought by Ukraine does not compare to the extent of death and destruction caused by Russia's daily attacks on its neighbour since the Kremlin launched the war in February 2022.
