Estonia has summoned Russia's ambassador over an airspace violation by a Russian military aircraft.

Foreign Ministry spokeswoman Mari-Liis Valter said Wednesday Estonia considers the violation serious. She said the Baltic country "demands an explanation" as to why a Russian Ilyushin-20 surveillance aircraft crossed into its airspace Tuesday afternoon.

Estonia's military said earlier the plane had entered Estonia's airspace for around one minute, before NATO fighter planes stationed in Lithuania intercepted it.

The incident comes as Russian forces have been accused of a series of border violations.

Since Friday, the Swedish Navy has been combing the Stockholm archipelago for signs of a foreign submarine that officials suspect entered its territorial waters illegally. It hasn't officially linked Russia to the suspected intrusion, but many analysts say Russia would be a likely culprit.