Two drones believed to be Ukrainian have come down in south-eastern Finland, Finnish media reported on Sunday.

Public broadcaster Yle reported that one unmanned aerial vehicle had fallen to the north of Kouvola and another to the east of the city. There were no reports of injuries or damage.

"Drones have strayed into Finnish territory. We take this very seriously," Defence Minister Antti Häkkänen said, according to Yle.

The ministry reported that a number of objects had been detected passing at low altitude through Finnish airspace. Combat jets were scrambled to identify them but had not shot them down to avoid damage on the ground, it said.

Yle said the air force had identified the objects as Ukrainian drones, and Prime Minister Petteri Orpo said later that they had "probably" originated from Ukraine. Orpo described the incident as serious and said it was being investigated.

Kouvola lies around 70 kilometres from the border to Russia's Leningrad region. Orpo said the drones could be linked to the overnight attacks on oil installations in the region.

Ukrainian drones have repeatedly strayed into the airspace of Russia's neighbours in the Baltic region and occasionally come down on their territories.

Ukrainian forces attacked installations in Ust-Luga, a Russian port on the Baltic Sea overnight, causing fires. Leningrad Governor Aleksandr Drozdenko confirmed the attacks and said Russian forces had downed 31 drones.

An air raid alert sounded in the Leningrad region on Sunday and Drosdenko warned on Telegram of the possible incursion of drones. He said internet speeds might be reduced, which is one of several ways to see off unmanned aircraft.