Russia's southern Rostov region, which borders Ukraine, was "subjected to a massive attack by the enemy", local governor Yuri Slyusar said on Telegram at around 6 am local time (0300 GMT).

"More than three dozen UAVs and three missiles" were deployed, he said, adding that the Russian air defence services were activated across several cities in the region.

While "most of the air targets were neutralised", a fire broke out at an oil refinery, he said

"Firefighters are currently fighting the fire," Slyusar said, adding that information was "still being clarified".

He said one person was wounded in a village near Rostov "due to the fall of drone fragments".

Russia's border regions have been hit frequently by Ukrainian fire, with two separate attacks last week targeting Rostov as well as western Bryansk region, sparking a fire at an oil depot and damaging an "industrial facility".

The latest attack came as Russian President Vladimir Putin was expected to hold his annual end-of-year news conference on Thursday.

He will address Russians as the conflict in Ukraine has escalated in recent weeks.