A Ukrainian drone strike appears to have damaged an icebreaker and an old Finnish building in Vyborg on Wednesday, some 40 kilometres from Finland's eastern border.

The four-storey Agricola building was built in Vyborg in 1902, when the city was still part of Finland.

An office of Russia's security service, the FSB, is located diagonally opposite the building.

Telegram accounts tracking the war in Ukraine said the FSB building may have been the intended target of the drone strike.

The Finnish Meteorological Institute (FMI) on Thursday recorded extremely poor air quality in South Karelia, including Imatra and Lappeenranta. Meteorologists said the worsened air quality was due to fires at Russian ports in addition to air particles travelling to Finland from central parts of the continent.

This week's Ukrainian drone strikes near Finland's border point to a significant shift, according to Jarmo Nieminen, a retired lieutenant colonel who has closely followed the war.

Nieminen said it is notable that an increasing number of drones have been able to travel hundreds of kilometres across Russia's most densely populated western regions.

Ukraine has struck targets in the Gulf of Finland before, but only sporadically. Now, its long-range strike capability appears to have become far more effective, he said.