The Finnish Navy said on Friday that its minelayer Hämeenmaa had inadvertently ventured a short distance into Russian territorial waters during a surveillance exercise on Thursday.
The vessel had been monitoring the territorial integrity of waters in the eastern part of the Gulf of Finland when it wandered about 600 metres into Russian territory.
When personnel manning the vessel noticed the error, they immediately returned to international waters and reported the incident in accordance with the operational chain of command, the Navy said in a statement.
Navy chief of staff Tuomas Tiilikainen told local news agency STT that the intrusion occurred west of Suursaari, an island in the eastern part of the gulf.
"Monitoring territorial integrity is our core mission. Our ships were there accordingly," Tiilikainen added.
The naval officer noted that the operation did not involve any kind provocation and explained that the vessel always has arms ready as is customary in monitoring missions.
The Navy said that it has launched a probe into the matter. Finland has also informed Russia and said that it regretted the incident.
