Three Russian border guards illegally crossed into the territory of Estonia on Wednesday, the Estonian Foreign Ministry said.
The ministry said the officers crossed the control line between Estonia and Russia on a breakwater in the Narva river.
They arrived at the site in a hovercraft, proceeded on foot along the river barrier, and later returned to their vehicle and crossed back to the Russian side.
The ministry published video footage recorded by a surveillance camera that it said documented the incident, which took place near the village of Vasknarva.
Estonian Interior Minister Igor Taro said the motives of the Russian border guards were unclear.
"There was no immediate security threat, but the police and border guards have significantly increased their presence and patrols," he said on Estonian television.
A meeting between representatives of the border guard authorities of both countries has been scheduled in response to the incident.
Estonia, an EU and NATO member, also said it would summon the chargé d'affaires of the Russian embassy in Tallinn and has demanded an explanation.
