A Ukrainian drone that crashed in Finland on Sunday carried an unexploded warhead according to a preliminary assessment, Finnish police said on Monday.

Finland reported a territorial violation in the country's southeast on Sunday after two Ukrainian drones crashed, marking the first time the Russia-Ukraine conflict has spilled onto Finnish soil.

"The UAV (Unmanned Aerial Vehicle) that came down north of Kouvola was found, in a preliminary assessment by the authorities, to have an unexploded warhead attached," police said in a statement.

The aircraft was later detonated in a controlled manner by Finnish authorities, police said.

It was identified by Finnish authorities as a large Ukrainian AN196 drone, which has a wingspan of 6.7 meters (22 ft) and is 4.4 meters long.